Transcriber's Note:

 This etext was produced from Astounding Stories November 1931. Extensive research did not uncover any evidence that the U. S. Copyright on this publication was renewed. 

 [Illustration: _The body went twisting and turning into the gulf below. _]

 Raiders Invisible

 By D. W. Hall

 * * * * *

[Sidenote: Alone and unaided, Pilot Travers copes with the invisiblefoes who have struck down America's great engine of war. ]

The muffled, helmeted figure of a pilot climbed down the spiderladder, nestled into the foremost scout's cockpit and pressed thestarting button. The motor spat out a wisp of smoke, then burst intoits full-throated roar: the automatic clamp above loosened: the scoutdropped plummet-like, bobbed to the flagship below, straightened outand zoomed six thousand feet up into the morning blue, where ithovered for a few moments like an eagle on taut wings. LieutenantChristopher Travers, the pilot, glanced around. 

Behind and below him was spread a magnificent panorama. Across theplate of scintillating glass that was the sea moved rows of toy ships, tipped by the gleaming, one-fifth-mile long shape of a dirigible, ofwhose three scout planes Chris's was the leader. As he watched, thesecond scout dropped from the plane rack beneath the dirigible's sleekunderside and went streaking away, followed by the third, in responseto the Admiral's order of: "Proceed ahead to locate the enemy'sposition. "

A grin relaxed Chris Travers' tanned, boyish face. His narrowed grayeyes swept the horizon. Below it somewhere lay hidden the ranks of theBlack Fleet, complete with its own destroyers, submarines, cruisers, battleships, aircraft carriers and the ZX-2, sister dirigible of theBlue Fleet's ZX-1. Chris spurted the scout ahead and murmured:

"This war game's goin' to be a big affair--the biggest yet!"

It was. The Atlantic Fleet of the United States Navy, termed "Blue"for convenience, had been assigned to guard the Panama Canal; thePacific Fleet, "Black, " to attack it. The cream of America's seaforces had been assembled for that week of March, 1935, all the wayfrom crabby little destroyers to the two newly completed monarchs ofthe air, the twin dirigibles, fresh from the hangars at Akron, athousand feet each in length and loaded with the latest offensive anddefensive devices developed by Government laboratories. 

[Illustration]

The war game around the Canal was planned for more than practice, however. The eyes of the whole world were on that array of America'socean might--the eyes of one foreign nation in particular. Washingtonknew of the policies of that nation, and wished to impress upon is thehopelessness of them. More than a game, this concentration of sea andair-borne fighting power was a gesture for the continued peace of theworld--a gesture strong with the hint of steel. 

Chris Travers was vaguely aware, through the rumors of the mess-room, of the double meaning of the game he was playing his part in, but thismorning he didn't give a single thought. He was too wrapped up in hisjob of spotting the van of the Black Fleet, radio-telephoning latitudeand longitude to the bridge of the Blue Fleet flagship, and gettinghome to his dirigible without being declared destroyed by one of thewar game umpires. 

Therefore, half an hour later, his heart thrilled as he glimpsed, wraith-like on the steely horizon, a wisp of smoke. 

 * * * * *

He catapulted forward, eyes steady on that hint of ships. The smokegrew to a cloud of black pouring from the funnels of a V-shaped squadof destroyers, rolling through the lazy swells of the Pacific waters. Behind them came the bulldogs, larger warships, hazy blurs in thedistance. 

Chris struck fist in palm to the tune of a gleeful chortle. He wasfirst! He hauled the microphone from its cubby in the dashboard andspoke the code words. Latitude, longitude and steaming direction ofthe Black Fleet he gave rapidly, and the information knifed back tothe bridge of the Blue Fleet flagship, a hundred miles behind, where awhite-haired admiral said: "Ah! Good boy! Get those bombersup--pronto!"

Chris commanded a superb view of the ZX-2, whose gleaming shape, showering rays of sunlight, hung like a thing in a painting over theBlack Fleet. He stared at the far-off dirigible, lost in admiration ofher trim lines, pausing a minute before returning to his own ZX-1. Atthat distance, the mammoth craft seemed no more than four inches long, yet, through his telescopic sight, he could discern her markings, machine-gun batteries and the airplane rack along her belly plainly. One plane, he saw, was suspended from the rack; the others werescouting for the Blue Fleet, even as he had scouted for the Black. Hewondered if something were wrong with the plane left behind. Somehow, it did not look quite familiar. 

But, even as he watched, it dropped from the automatic rack, thenstraightened and soared dizzily up. And, from one of the airplanecarriers' broad decks, he saw two pursuit craft begin to rise. Hegrinned. They'd seen him, were coming after him!

He gripped the stick, prepared to swerve around. He had already raiseda spread-fingered hand for a derisive parting gesture, when suddenlyhe stiffened. The hand dropped as if paralyzed. 

"Good Lord!" he gasped. "What--"

The mighty thousand-foot dirigible ZX-2, pride of the Navy and allAmerica, had wobbled drunkenly in her path. She stuck her nose down, and then her whole vast frame shivered like a wind-whipped leaf as thedull roar of an explosion rolled over the sea. A huge sliver of hidewas stripped from her as if by magic, revealing the skeleton ofgirders inside--revealing a tongue of crimson that licked out andwelled into a hell of flame. 

Chris's blood froze. He watched the ZX-2 wallow in her death throes, writhe in the fiery doom that had struck her in seconds, that wasdevouring her with awful rapidity while thousands of men, blanched andtrembling, gazed on helplessly. He saw her plunge, a blazing inferno, into the sea beneath. .. . 

There were old pals on her--buddies, gone in a flash of time!

This wasn't a war game. This was tragedy, stark before his eyes. 

 * * * * *

The Black Fleet forgot its mimic battle. Radio telephone messageswinged over the horizon to the approaching Blue Fleet. The Blackdreadnoughts hove to; launches with ashen-faced men in white manningthem dropped overboard; a dozen destroyers rolled in the swells arounda crumbled, charred egg-shell that but minutes before had been anomnipotent giant of the sky. 

Chris Travers, aloft in sunlight suddenly bereft of its beauty, jammedthe stick of the scout full over. He could do nothing, he knew. Hecould only return to the ZX-1 and tell the story of its sister as hehad seen it. 

But why, he wondered as he flew almost blindly, had the ZX-2 soquickly flamed to oblivion? The helium of its inner bags bad beenuninflammable, as had the heavy oil of its fuel tanks; the ten engineswere Diesels, and hence without the ordinary ignition system andgasoline. Safety devices by the score bad been installed on board;nothing had been overlooked. And the weather, perfect. 

It was uncanny. It seemed totally unexplainable. 

Swarms of planes droned between sea and sky, all speeding in the onedirection, west, to where the crumpled remnants of a dirigible wereslipping quickly beneath the billows, beyond the sight of man. Planesof war game umpires, of officials, of newspaper correspondents andphotographers. And soon a spectral, gleaming wisp of silver nosed outof the east, and the lone scout flying east dropped in altitude tomeet its mother. 

Mechanically, his mind elsewhere, Chris shoved the button which rearedthe automatic clamp behind the cockpit in preparation for affixing thescout to the plane rack beneath the ZX-1. The dirigible, far inadvance of the Blue Fleet, was roaring along at its full one hundredand fifty to hover over the grave of its sister. Chris eyed its courseand changed his. To jockey into the rack, he had to pass the dirigibleand come up underneath from its rear. 

 * * * * *

The air giant roared closer. As the distance between then loosened, Chris's brow wrinkled and he swore softly in puzzlement. 

"Now, just what's wrong with them?" he exclaimed, "The darned zepisn't flying straight! She's wobbling in her course!"

It was hardly apparent, but true. Ever so slightly, the snub nose ofthe ZX-1 was swaying from side to side as it sped through the air;ever so slightly, her massive stern directional-rudders were wavering. 

She was less than a mile away now. At that time, there were no otherplanes in sight; none flying in that vicinity save Chris's. He gluedhis eyes to the telescopic sight. A moment later, sheer horror swepthis face. 

"_Good God!_"

The scout leaped as its throttle rammed down. The gleaming, thousand-foot shell of the ZX-1 roared by it at equal altitude, makingit a puny fly-speck in the sky. But the fly-speck was faster. Itturned in a screaming bank; it straightened; it lunged back after theswaying, retreating mammoth like a whippet, lower, now, than itsquarry. It maneuvered expertly as it gained, for one of the bestpilots of the service was at its controls, and there were deep linesgraven in his face, lines of anguish and intolerable suspense. 

Through the telescopic sight, Chris had not seen a single white-cladfigure standing beside the glass ports of the dirigible's control car. But he had seen, slung from the rack along her belly, a singleplane--the same rather peculiar-looking plane he had seen hangingbeneath the rack of the ZX-2 a few minutes before she had gone down inflames!

And in that plane, he knew surely, was the answer to the mystery. 

 * * * * *

Speed cut to just a trifle more than the dirigible's. Chris passed afew feet underneath the huge expanse of her lower directional rudder. From so close, its uncontrolled wavering was terrifying. 

His faculties were concentrated on the task of sliding the scout'sclamp into the groove of the plane rack, but he was also surveying thelone airplane hanging from it. A powerful machine, painted in Navycolors, a peculiar knob on the upper side of each half of the top winggave it its unfamiliar appearance. Its pilot was obviously aboard thedirigible, working. .. . 

Closer and closer the scout crept, quarter-way now along from thestern of the massive bulk that loomed above it, and within fifty feetof the third clamp in the rack. Touchy work, maneuvering into it, withthe ZX-1 yawing as she was, and the need for haste desperate. Chris'shands were glued to the stick: his nerves were as tight as violinstrings. Then, when only ten feet from the rack clamp, he gave astartled jump of uncomprehending amazement. 

The propeller of the mysterious plane ahead had roared over. Its clamphad left the rack; it had dropped down in a perfectly controlled diveand flattened out as if a master pilot were at its controls. 

But the plane's cockpit was still empty, Chris could see; nor had heseen any figure pass down the ladder from the dirigible into it!

Devoid of all emotion save bewilderment, he sat stupidly in the scout. A moment later, so well had he aimed it, its clamp nestled snugly intothe groove of the rack, and the regular automatic action took place. Atiny door slid open directly above in the dirigible's hull: a thinladder craned down--and Chris's nostrils caught a faint whiff ofsomething that cleared his mind of its confusion instantly. 

Just a whiff, but it registered. Gas, with an odor resembling carbonmonoxide. 

He stared up. Over the edge of the automatic trap-door above, awhite, contorted face was hanging. The dirigible swung; white-cladshoulders and body slumped into view. Then, with a rush, the bodyslipped through, jarred against the connecting ladder, slithered offand went twisting and turning into the gulf below. 

"God!"

Gassed! How, by what, Chris had no idea. A moment before he had beenabout to follow the uncannily piloted plane; but now his duty wasplain. He knew with awful certainty that in minutes, seconds perhaps, the giant ZX-1 was scheduled to roar into flames like its sister andplunge into the Pacific. 

He jerked out a gas mask. He was fitting it on with one hand as, withthe other, he hauled himself up the spider ladder into the hull of thethundering, yawing dirigible. 

He did not see, hovering a few hundred yards behind the ZX-1, themystery plane; he did not see it now begin to approach the rack oncemore. 

 * * * * *

The crew of that dirigible of death, Chris discovered, had not had achance. White-clad bodies lay sprawled throughout the cabin whichcontained the mechanism of the plane rack, stricken down silently attheir posts. There was no life, no sound save the booming of themotors and the whip of the wind screaming past the uncontrolled airtitan. 

But he did not pause there. He did not know what he was grapplingwith--it seemed black magic--but he darted to a ladder which angled upfrom the lowermost entrance cabin to the cat-walk that stretched fromthe nose to the stern of the ship. If any infernal contrivance hadbeen planted aboard, it would be in the most vital spot. 

Heart pumping from the artificial air he was breathing and from theconsciousness that each second might well be his last, he sprintedalong the interior gangway. Above was the vasty gloom of the gas bagsand the interweaving latticework of the supporting girders; the drumof power-car motors and the strained creakings of cables and supportsechoed weirdly throughout. Outside was the sun and the sea and theclean air, but this realm of mammoth shapes and dimness seemed apartfrom the world. Once he stumbled against something soft andyielding--a body flung down there in death, fingers at its throat. Andthere were other white-clad figures, grimly marking off the length ofthe cat-walk. .. . 

Chris's nerves were raw and his face sopping with sweat beneath itsmask when suddenly he stopped at sight of something that lay on thecat-walk, with the main fuel tanks on the girders just above it andthe entrance to the control car just below. 

 * * * * *

It was a black box, perhaps two feet square and a foot in depth, madeof dull metal that did not reflect the rays of the light bulb placedat the head of the ladder leading down in the control car. There werethree curious little dials on its face, and the trembling finger ofeach one was mounting. 

It had been strategically placed. An explosion at that point would ripopen the fuel tanks, split the largest gas bag, wreak havoc on anintricate cluster of main girders, and destroy the control car withits mechanism. 

"No wonder the ZX-2 crashed!" Chris muttered. 

Then his hands swept down. The next instant he was hugging the thingtight to his chest and stumbling down into the control car, hearingonly a high-pitched, impatient whine that was coming from the box asthe fingers of its dials crept slowly upward. 

The ZX-1 was wavering wildly as her rudders flopped from side to side, and with every swing the bodies that lay in her control car, strangledby gas, stirred slightly. The gray-haired commander was stretchedthere, one arm limply rolling as his ship, which had gone so suddenlyfrom him, rolled. Subordinate officers were tumbled around him. Deathrode the control car. 

But down to it and through it now came one who was alive, a figuremade grotesque by the mask it wore and the pack of the parachutestrapped to it, who threaded past the littered bodies, an ever-risingwhine wailing from the box clasped in his arms. 

With a leap, he was at one of the car's port-holes, fingers fumblingat the heavy bolts. The seconds seemed eternal, and the box's whinehad become a shattering, sinister scream when at last the boltsloosened. The round pane of glass teetered back, swung open--and themasked man slung his metal burden out, out from the ZX-1 into the gulfbetween sea and sky. 

It arced through the sunlight, went spinning down, became a dot, itsscreaming faded. Then something synchronized within it, and it wasgone--in a burst of weird, bluish light, whose fangs forked upwardsfor a second, their unearthly flash dimming even the sunlight, andthen were gone, too. .. . 

 * * * * *

Chris found that his whole body was shaking. For a moment he stoodthere with his masked face through the port. 

"Damn close, " he muttered. "But what was it that left the box here?"

Then he jarred against the side of the car as the ship swung and cameback to realization of what was needed to be done, and done at once. He shifted his gaze, drew his head back, and thrust it forth again, staring. 

"Good Lord!" he cried. "That plane's come back!"

His own craft was not alone under the rack. The same mysteriousmachine hung there again, its cockpit empty, and the automatic spiderladder was stretched down to it from the trap-door in the dirigibleabove. 

"Whatever flies it is aboard now. " Chris thought aloud. "But it gotback too late to stop me. Well, this time--"

He felt uneasy, however, almost powerless. What was this thing thathad wiped out the crews of two dirigibles with deadly gas, and wreckedone of them? He spun around. The control car looked the same. But whatmight be moving in it?. .. 

Chris carried no gun; but he extracted the service repeater from theholster of a body at his feet. Gripping it, he leaped to the helm ofthe dirigible. It was the work of a moment to clamp on the mechanical"iron mike, " which steadied the ZX-1's mad swaying and leveled herahead in a dead straight course. He could not cut down her speed, unless he went to each one of the hull-enclosed engine stations, andmore urgent work awaited before he could afford to do that--work ofsending out an S. O. S. Before the weird, unseen killer and wrecker cameto grips with him. 

Though seeming hours, only minutes had passed since he had tooled hisscout into the rack. Ahead, he could see the smudge of the BlackFleet's smoke on the horizon. Not so very far away, but a lot couldhappen in the distance still separating dirigible and surface craft. 

 * * * * *

He ran back into the radio-telephone cubby, which was a division ofthe control car. The operator was sprawled there, limp in his seatbefore the shining, switch-studded panel. Chris removed the head-gearof ear-phones: then he hauled one of the cubby's port-holes open, letting in a rush of cleansing air. His fingers sped quickly over thepanel; a row of tubes glowed; the machinery hummed. Chris jerked offhis mask. 

A last faint odor was present, but he hardly noticed it, for his lipswere at the mouthpiece and he was thrusting out a call for help. 

"ZX-1 calling . .. ZX-1 calling . .. ZX-1--Hello!"

An answer from the flagship of the Black Fleet ahead had sounded. 

"This is Travers, pilot on the ZX-1, speaking. We're coming dead foryou; full speed; you'll see us in minutes. Get some planes with mencapable of handling the dirigible up here immediately. The wholecrew's been laid out by gas; there was a contrivance planted aboard toblow up the ship and send it down in flames as the ZX-2 was. The thingthat did it--"

_Crack!_

A gun barked out from behind; something crashed and splintered on theradio panel. Chris felt a white-hot needle sear along the side of hishead. His brain reeled; with everything dancing queerly before him insplotches of gray and black he toppled down off the seat, knowing theradio-telephone had been put out of commission by the cessation ofsound in the ear-phones clamped to him. 

He gripped his consciousness hard. It was like a delirium: he waslying sprawled beside the seat, twisted round so that he saw, hangingin the cubby's entrance door, an automatic, dribbling a wisp ofsmoke--the automatic that had just fired, but hanging there by itself, held by something he could not see!

He was only half conscious, for the scorching pain along his head wasthrobbing his brain dizzily, but he realized that the service repeaterhe had taken from the control car lay by his side, within easy reach. But, while on the verge of risking a wild grab for it, he heard avoice, speaking very softly and with a slight thickness of accent. 

"Do not move, " it said. "I fire if you do. Now, listen: What did youdo with the box that you found? Tell me quick, or die. "

It was fantastic, unreal. There was--nothing, and yet a man, living, breathing, but invisible, was speaking! Chris could not understand;but it was at least a little relief to know he had a human to dealwith. For with humans, strategy can be used. .. . 

 * * * * *

He groaned. He saw plainly that the unseen marauder had been aboardwhen he had thrown the box over, and thus had not seen it explode inmidair: did not know whether it had been tossed out or merely renderedharmless by being tampered with. If only the latter, it could bequickly repaired and set again. That must be the invisible man'sreasoning. 

Again Chris groaned. He moved an arm weakly and whispered:

"Can't speak much. Come closer. "

The service repeater was very close now to his right hand. And he felta thrill when he saw the automatic come forward through the air, descend, and pause right next to his head. He sensed a man closebehind him, and he heard:

"Well? Tell me, quick. Did you throw it over, or--?"

"Don't shoot!" Chris groaned. "I'll tell you. I didn't--throw it over. I took it apart to get the secret of it. I put it--there. "

He pointed feebly with his right hand, thus leading the invisible manto turn his head. His legs braced imperceptibly. And then:

"Like hell!" roared Chris Travers, and shot his whole weightbackwards, grasping the service gun, whipping it around and yankingthe trigger three times at the same instant. 

Shooting at nothing! But, even above the bunched roar of theexplosions, there pierced out a howl of agony that died quickly to asobbing moan. Chris saw the automatic drop to the floor, felt theinvisible body he had crashed into jerk away. He jumped to his feet, clutched at that body, and caught thin air. He swung around, listening, the service repeater in his hand. 

Out of the air somewhere before him there came the sound of low, racking gasps, and also the slow noise of feet dragging heavilytowards the cubby's door, towards the ladder that led up to thefore-and-aft cat-walk. 

Chris sprang, slashing the butt of the gun downwards. The lead wasfalse. He hurtled jarringly into the door jamb, the gun thumpingagainst the floor. The wind was knocked from him; the nausea of hiswound swept him again with a surge of dizziness. But the painfulscuffle of unseen feet ahead pulled him up once more; like apunch-drunk fighter he staggered out from the cubby to the ladder andhauled himself up the steps. He half-fell at the top, but his mind wasclearing; and as he swayed there he knew what he had to do--saw theduty that lay before him. .. . 

More slowly, he crawled after the dragging footsteps and the gasps ofthe invisible raider, following them through the vast dimness of theinterior of the dirigible ZX-1. 

 * * * * *

The chief operator on duty in the flagship of the Black Fleet swunground in his seat and yelled through into the bridge of the massivebattleship:

"Urgent, sir! From the ZX-1!"

A moment later the captain of the ship, for the fleet's admiral wasout in a launch inspecting what little of the fallen ZX-2 was stillfloating on the surface, was at the operator's side, listeningamazedly. 

The operator read off, word for word, what Chris Travers had sent. ". .. There was a contrivance planted aboard to blow up the ship andsend it down in flames as the ZX-2 was. The thing that did it is--" hefinished, and fell silent on that uncompleted sentence. 

The captain's lined face expressed incredulity. "My God!" he burstout. "First the ZX-2, now-- That all?"

"Yes, sir. I can't get any answer or connection. "

They stared at each other. Finally the captain spluttered:

"Is some maniac loose in this fleet? Don't sit there like a fool, man!Get in touch with the _Saratoga_; tell 'em what you received; tell 'emto send some men up to that dirigible, wherever she is. We can't loseboth of them!"

The operator's fingers skipped nimbly; even while he was speaking intothe microphone, the red-faced captain had rushed back into the controlbridge and was roaring:

"Signal the Admiral back here! Hurry!"

 * * * * *

Things moved quickly then; small things, but significant. A casual eyeglancing over the ranks of the Black Fleet as it lay around the sceneof the tragedy, waiting for orders, would not have noticed anydifference. The launch containing the fleet's admiral, which had beenfussing about with its load of officers and various dignitaries, suddenly wheeled and pointed back for the mammoth flagship, inresponse to swift signals from the arms of a gob on her bridge; and, on the broad landing deck of the carrier, _Saratoga_, two three-seaterplanes, equipped with automatic clamps for a dirigible's rack, werewheeled up to the line. 

Their props were spun over. But even before their cockpits had beenfilled, an officer on the bridge of the flagship, and a dozen othersthroughout the fleet, cried:

"There she is!"

Over the eastern horizon, a gleaming sliver in the sunlight, thunderedthe ZX-1, straight for the array of the Black Fleet. Only a few menwere aware of the drama-fraught message which had come down from herradio cubby, but her growing shape commanded the eyes of every sailorand officer alike who had time to watch. A few telescopic sights weretrained on her as she bellowed ahead; the keen old eyes of a veryperplexed and puzzled admiral were at one of them. 

"Two planes hanging from her rack, " he muttered, half to himself andhalf to the officers standing around him. "Both Navy. Say, they'redropping off! Not coming this way, either. Going northeast. Fast, too. Can't see 'em any more. .. . Those men getting up from the _Saratoga_?Good. We'll find out something soon. Here she comes!"

Closer and closer roared the dirigible. Two planes from the _Saratoga_were swooping up to enter her rack, but the other two planes thatshortly before had been suspended from it were gone--already vanishedinto the northeast. 

"Don't understand this at all!" said the Admiral of the Black, orPacific, Fleet of the United States Navy. 

 * * * * *

Things had broken well, Chris Travers considered. He had only woundedthe invisible raider; but, luckily, had wounded him badly, so that, evidently, just one object was in the man's mind: to get back to wherehe came from, to where he could find help. He seemed oblivious of thescout that was following behind at the full speed of its mighty rotarymotor, following him to his base, wherever it was. 

"Just as well I didn't kill him, " Chris muttered. 

The rush of wind had cleared his brain; his faculties were steady andnormal. Not so with the man in the plane he pursued. It was flyingcrazily, but clinging to one course, nevertheless--into the northeast, towards land, some two hundred and fifty miles over the horizon. 

The great silver shape of the ZX-1, barren, now, of life, droppedaway, speeding ever due west; the hazy dots and blur of smoke whichdenoted the motionless Black Fleet vanished. But Chris was in contactwith the fleet's flagship once more, through the compactradio-telephone set of his scout. As he flew, his eyes fixed steadilyon the plane ahead, he was rapping into the microphone the story ofwhat had happened. He told of the invisibility of the strangemarauder, of how accurately he had judged the time of his raids; ofhow he, Chris, had managed to prevent the destruction of the ZX-1. 

"He uses a tremendously expansive gas resembling carbon monoxide, " hewent on. "It seeps into every cranny of the dirigible, killingeverything. The crews got no warning; they didn't know what washappening; couldn't see him! Well, I managed to wound him on the ZX-1. He beat it. I'm following him. If he lasts out, he'll go to where hecame from, and we'll find out who's in back of all this. Let you knowwhere his base is soon as I get there. Keep listening. Okay? Right;signing off. "

Silence, then, between the scout and the flagship far behind. .. . 

 * * * * *

On--on Time passed. The scout's gas was down below the half-way mark. They had covered two hundred miles now at a speed just bordering threehundred. The plane ahead looked uncanny with its apparently emptycockpit, but Chris could see all too well that death was pressing atits invisible pilot. The big machine was literally staggering in itscourse as the hands on its control stick grew weaker; was yawingwildly, even as the ZX-1 had yawed after her crew had been slain byvapors they could not see. 

"He's got to last out!" Chris muttered. "Got to!"

At that moment land appeared, and the fleeing plane altered itsnortheast course to due east with an abrupt jerk. 

First it was a mere hazy line on the horizon; then it rose to a thrustof land, jutted with cloud-misted hill-tops. Then, as the two roaringspecks that were airplanes came closer, heavy tropical foliage becamedistinct, and white slashes of surf breaking on the shore. This wasthe Azuero Peninsula, most western point of the Republic of Panama. 

Aside from one small cluster of wretched huts, it was practicallyuninhabited. Guarded by dense growth, only one or two of the dustypaths which passed for roads wandered aimlessly through its tangledcreepers, trees and bush. To the southeast was the broad Gulf ofPanama, doorway to the Canal; on the other sides this thumb of landwas surrounded by the reaches of the Pacific. 

The plane was obviously nearing its eyrie--dropping lower and lower, losing speed and altitude; and also threatening each moment to tumbledown out of control into the smothering welter of olive-green below, with a dead, unseen body in its cockpit. 

But where was the landing field? They were now over the very heart ofthe Peninsula, and still Chris, searching through his telescopicsight, could see nothing but the monotonous roll of jungle. They mustcome to it soon, or be over to the Caribbean Sea and the MosquitoGulf. 

Then suddenly he started forward, staring. Of course there was nolanding field in sight. The mystery plane needed none. It possessedthe power of the helicopter: it could rise straight up or sinkstraight down. 

From each one of the two knob-like projections on its upper wing thathad puzzled him previously, a propeller had risen and unfolded intolong, flat blades. They whirled in circles of light in the sun; andthe airplane beneath them poised, all but motionless, its mainpropeller swinging idly, and then began slowly to drop downwards. 

But Chris, swooping nearby, was still perplexed. Dropping down towhat? There was only the dense tropical growth beneath. He could seeno trace of men, no clearing, however small, no base--nothing but thejungle. 

"How in the dickens--" he began; and then stopped. At that moment thejungle's secret was revealed. 

 * * * * *

As the helicopter-plane dropped to within a few hundred feet of it, astrip of the sea verdure split in two and reared up. It looked, atfirst, like magic. But from aloft Chris saw the trick and how thecamouflage was worked. What appeared to be a slice of the jungle roofwas, in reality, a metal framework cunningly plastered with layers ofgreen growth. An oblong, some fifty by a hundred feet, it parted inthe middle like a bridge that opens to let a steamer through, revealing the lair of the plane. 

Soon more was revealed. Two tiny, green-painted huts stood in theminute clearing, and a few white-clad figures were by them, staring upat the plane sinking down and at the other plane which soared abovelike a buzzing mosquito. 

One of the dwarfed figures in white waved an arm. The others aroundhim darted into the left-side hut. Then the helicopter-plane's wheelstouched the small space allotted for it in the clearing, and thewhirling propellers halted. 

"So that's the secret!" Chris muttered. He pulled the microphone ofthe radio-telephone to his lips and angled with the dials forconnection with the fleet hundreds of miles behind, meanwhile notinghis exact position on Azuero Peninsula. But before he spoke, somesixth sense bade him glance below once more. 

An icy shiver gripped his body. 

A thin slit had appeared in the roof of the left-side hut. A spot ofbright blue light was winking evilly inside it. And, though he couldnot hear it, Chris knew with terrible certainty that a shrill, impatient whining was piercing from the machinery of a weapon insidethat hut--a weapon whose fangs had forked close to him once before--aweapon which the winking eye of blue presaged. 

It struck. But at the same instant Chris leaped desperately from thecockpit of the scout. 

 * * * * *

He leaped almost into the teeth of the blue-tinged ray which knifed upwith uncanny accuracy from the slit in the roof of the hut. He wasconscious of a flash of unearthly light, of terrible heat which camewith it. Only the force of his jump saved him. He pulled the ripcordof the 'chute strapped to him and jerked to a pause; then he wasswinging beneath a mushroom of white, trembling as he stared at thefate he had missed by a hair's breadth. 

A web of spectral blue light had enveloped the abandoned scout. Theplane appeared to shudder, hanging almost motionless in thewraith-like mist. Then, with a crackle, the wings and tail shiveredinto countless fragments; the stripped fuselage nosed over and plungedearthward, a roaring mass of flames. A fiery comet, it screamed pastthe man who swayed beneath his 'chute, coming within a few hundredfeet of him and searing him with its hot breath. Then it drove intothe dense flanks of the jungle growth. 

Soon only a charred skeleton marked the last landing field of a scoutof the dirigible ZX-1. 

"And now, I guess, " Chris whispered, "they'll turn that ray on me. .. . "

But he had only been a thousand feet up when he jumped. Already he wasclose to the top of the jungle. The clearing and its huts disappearedfrom view; he was out of range of the swift-striking ray. And, hereflected, though the scout was gone, he was still free--and could getto the Canal. .. . 

But tropical growth is difficult to land in. 

A moment later his swinging body crashed through the branches of atree, and he pitched forward, unable to control the impetus. A suddenshock of pain stabbed through his head and everything spun dizzilybefore him. He knew he was falling, jerking down as the parachuteripped on the boughs. There was another impact which drove allremaining consciousness from him. 

Darkness washed over Chris Travers, lying limp beneath the shreds of asilky white shroud. .. . 

 * * * * *

Electric light. A strong glare of it somewhere. A dull throbbing inhis head. Then, a voice, with queer, hissing s's, speaking very closeto him. 

"Ah, yess. Look you, Kashtanov. He will be conscious soon, I think. "

"You're a damned fool, Istafiev, to let him wake up, " said anothervoice, cool and of easy correctness. "He'll see the machines. Andthese Americans are tricky--one can never tell. "

"Tricky? Bah! This fellow is a service man; there are things I canlearn from him. Come, now, wake yourself properly, you! That glass ofwater, throw it on his face. "

Kashtanov--Istafiev. Names that could belong to only one country, tothat huge power overseas which was hovering, so said rumors, on thebrink of war, waiting only for a favorable opportunity to strike--thecountry which the war game around the Canal had been designed toimpress. Chris Travers' mind cleared just then with completecomprehension of who had schemed to send both dirigibles down and whohad built this secret lair on Azuero Peninsula. 

Inwardly, he groaned. It was all too plain. The destruction of theZX-2 and the thwarted destruction of her sister had only been thefirst step of some gigantic plan which was to provide the opportunityfor the mighty fighting machine overseas to strike. And he, who mighthave balked it, had made a rotten landing from the scout and deliveredhimself, helpless by his own clumsiness, into the hands of these men. The self-accusation was bitter. 

With their secret of invisibility, their deadly blue rays, what havoccouldn't they wreak, working from their cunningly concealed base?

And now they were waiting for him to recover consciousness--waiting toquestion him before killing him. .. . 

But as he lay there, apparently still senseless, Chris was grapplingwith the seemingly hopeless problem. So, even when he felt thetingling coldness of a spray of water on his cheeks, not one line ofhis face moved, nor did the tiniest flutter of eyelids betray him. 

Although the fumbled landing in the jungle had been a catastrophe, ithad granted him his only weapon. He was believed to be genuinelyunconscious. 

"Another--he iss stubborn, " hissed the voice of the man calledIstafiev. "His senses will soon come. I can bring them back--oh, yess!"

"Enough of this!" complained the suave, beautifully modulated voice. "Darkness is coming; there's a lot to be done. Shoot him and throw himout!"

"It iss I who am in command here, comrade Kashtanov. Remember that. Idesire to speak to this man. There! No? No sign yet? Well! We willsee if this helps those eyes of yours to open, my American!"

Then began sheer torture. 

 * * * * *

It was an ordeal of silence. By no motion, sound or slightest sign ofconsciousness could he seek relief. Inanimate Chris Travers lay, holding his pose sturdily, although it seemed that the sweat wasspurting from the pores, while a thin, cruel knife-blade drove intothe quivering nerves beneath his left thumb-nail. 

Deeper and deeper it inched, accompanied by the soft breathing of theman who guided it, until Chris felt one great sob of pain welling upinside him, struggling to break past his lips; felt a tremendous urgeto writhe, to break away from the digging steel. His tongue seemed tobe trembling, shivering; but no other part of his body, not even thesmallest flicker of eyelash, betrayed him. At long last there came avoice, sounding as if from miles away, and the disgust in it was verygood to Lieutenant Christopher Travers. 

"Bah! It iss no use. His thick skull must be fractured. I could cuthim open and he would not awake. He might be conscious for minutesafter some hours--no, do not shoot him. I shall learn a few detailsfrom him then. Throw him over there. Now--Zenalishin iss dead, but themask and cylinder on him should be returned to visibility. Well, wewill return him, too. Then, Kashtanov, to your instructions and yourwork. "

Hands gripped Chris's body. He felt himself thud against a wall, andslumped into a heap, head lolling over. The cessation of pain wassweet, though his thumb was raw, but sweeter still was the knowledgethat he had won the first tussle: that he was deemed to be harmlesslyunconscious for hours. 

And carefully, through his lashes, he permitted himself a glimpse ofthe room he lay in, and the men whom he had heard and felt but not yetseen. 

 * * * * *

It seemed more like the belly of a submarine than a room, that maze oftubes, levers, wheels, switchboards and queer metallic shapes; and theblur cast upon his vision by barely raised eyelashes made it appeardoubly unreal and grotesque. It might have been another world. 

Some of it was recognizable. A massive radio-telephone set, by which, he judged, all communications between the fleets in the Pacific wereoverheard; a squat dynamo; a set of huge cylinders, from which, probably, had come the highly expansive gas that had snuffed out thecrews of the two dirigibles. But there were other things--strange, monstrous. One of them, the tapered tube of metal that angled up tothe hut's ceiling, its base a mass of wheels and dials and tubing, wasevidently the weapon of the ray that had struck the scout down. 

There were three men visible in the room, and Chris switched hisattention now to them. 

Two were standing by a table in the center of the room, directly undera shaft of light from a powerful electric bulb. The shorter of themwas saying to a third man, who knelt in front of the dynamo:

"On full. " Then, as a full-throated drone pulsed from it: "Zenalishiniss there? Yess. Put him in. "

The voice of the hissing s's--that was Istafiev. Short, stocky, black-haired, he was a direct contrast to the tall figure next him ofone whose pointed black beard gave elegance to sharp, thin features. He carried a gun at his waist, and he identified himself as Kashtanovby saying languidly:

"Better strap him in. He'll fall, otherwise. Get some cord; I'll lifthim. "

The other man, by the dynamo, apparently a subordinate mechanic, dull-faced, drew a loop of cord from a box nearby, while Kashtanovwent through actions that seemed fantastic. He stooped, groped alongthe floor, and then gripped what looked like thin air with his fingersand lifted upwards. But it wasn't air, Chris knew; it was theinvisible body of a man--the man who had destroyed the ZX-2, the manwhom he had shot at in the cubby of the ZX-1--whose invisibility wasnow to be stripped from him. 

By what? Carefully Chris swivelled his gaze around until it caught onan object which dwarfed Istafiev, now waiting by its side with onehand on the small panel of a switchboard. 

 * * * * *

A strange thing, truly, to find in a little hut on Azuero Peninsula!Row upon row of slender curved tubes, describing a three-quarter ovoidso that there was an opening for entrance in front, rose to a heightof some eight feet, the whole topped by a curious glassy dome whichwas filled with creamy substance. There was room inside the layers oftubes for a man's body to stand upright--and a man's body was uprightin it now, held by cords strapped to his unseen arms. 

Invisibility! The dream of scientists for years! Here created, heretaken away--by the simple manipulation of two levers on the controlpanel. 

Intently Chris watched Istafiev pull down the right-side lever. 

As it came down, the creamy liquid in the dome above the cage began toswirl slowly, then to froth and boil and whip round and round, whilethick, dropsical bubbles slid up from its heaving surface and burst, discharging a kind of grayish mist, under which the white substancesank, until there was nothing left in the dome but drab-colored vapor. On the completion of this stage, the layers of tubes below warmedinto life. They glowed with a soft vari-colored brightness that filledthe cage with a golden splendor and seemed to rim each one of thewatching men with fire. 

"See you, Kashtanov, " came Istafiev's voice. "The refractive index, lowered to that of air to produce invisibility, iss being raisedagain--all through a simple adaptation of Roentgen's theories! Thesubstance above, mark, in the dome, which this morning you saw affectZenalishin's blood and the pigment of his hair so that the vibrationswould render his colorless tissues transparent, iss now reversing. Soon--see!--already he becomes visible!"

Something was growing in the heart of the ribbons of color, and Chrisstrained his shrouded eyes to discern what it was. 

Black lines, standing out in the dazzling welter of light--lines thatgrew and became more solid as he peered at them--lines that wereshaping into a recognizable form, the form of a man's skeleton!

The effect was that of an X-ray. A skeleton hung in the cage, heldsteady by the cords around its arms, its naked skull with yawningeye-pits grinning out at the four men in the room. Soon other detailsbecame visible: black lumps that were organs, the web of fine thinlines that were veins; and then a hazy, ghostly outline of flesh thatquickly assumed solidity, burying the bones and veins and organs whichhad been first apparent. 

 * * * * *

And all the time the dynamo was filling the hut with its sweepingdrone, and the million points of light flung from the intercrossingflame-tongues inside the cage were dancing madly on the walls andfloor and ceiling, making the whole scene unreal, fantastic, as from adream. .. . 

"There! That iss enough, " said Istafiev. 

The lever went back. The streaks of blue-white that threaded the cagedied; the grayish vapor in the dome above faded away, leaving more ofthe creamy, bleaching substance than had been there originally; thedynamo was shut off, and silence fell in the room. A naked man with avery white, peaked face and a blotch of blood encrimsoning his neckhung inside the cage, his head pitched over lifelessly to one side. 

Chris stared, almost forgetting the pose of unconsciousness in hisbewilderment. A queer mechanism shaped in the form of a cylinder fromsome oddly sparkling, almost transparent material, was clasped to thenude body's chest: over the nose and mouth was another smallattachment of the same substance. A nozzle midway in the largecylinder's front side gave him the clue: from it, obviously, had comethe gas which had strangled the crews of the dirigibles, and thecovering over nose and mouth was a novel gas mask. The material theywere made of could, obviously, be rendered invisible--a virtue notpossessed by ordinary inorganic substances. Invisible death from aninvisible container, carried by an invisible man!

"Yess, dead, " hissed Istafiev, probing the motionless, naked body. "Hejust got here, told what had happened, and died. He was hurt too badlyto think of taking off the gas cylinder or putting on a coat. Well, itmakes no difference. .. . Here, Grigory, take off the mask and cylinderand bury him. And you, Kashtanov, look well at this. "

From the table, he picked up a large white piece of cardboard andtapped it meaningly. There were two broad lines on it, running side byside through other smaller lines and shaded patches, and there wasalso a thick black arrow pointing to one particular place on it. 

The chart was easy to understand. Chris Travers recognized itimmediately, and his heart seemed to stop for a moment as he did. 

Their first step had been the dirigibles: their second was a blowwhich paled the other into insignificance. And Chris told himselfdesperately:

"It can't go through! It can't!"

The lines on the cardboard were a detailed map of the Panama Canal;and the black arrow pointed unerringly to its most vulnerable, unguarded and vital point, the Gatun Spillway, which, if wrecked, would put the whole intricate Canal hopelessly out of commission. 

 * * * * *

Istafiev was speaking again, in low, terse tones, oblivious of thedesperate resolve forming in Chris's brain. 

"Only one of the dirigibles had been destroyed. Well, it iss too bad, but not fatal to the plan. The ZX-1 can hamper our country'soperations when she strikes, but if the ZX-2 were also in action, theywould be hampered much more--perhaps fatally. It iss not serious. Sowe go ahead. Now, Kashtanov, for the last time, the scheme of wreckingGatun Spillway iss this:

"Note, here, the small golf course. That iss your landing space. Youknow its location: a mile, perhaps, from Gatun Dam and the spillway. At night, there iss no one near it or on it. You drop down to the golfcourse from seven thousand feet: the helicopter motors are muffled, and no one will hear you come. Some of the stretches of the course aresecluded and hidden by the surrounding jungle; choose one of these toland on. Well, that iss easy. 

"The spillway iss about midway in Gatun Dam: its channel has been cutthrough a hill. You come along the side of this channel right up closeto the spillway--close, remember!--and leave the box there. The rangeof the rays, you know, iss two hundred feet: set them to fire oneminute after you leave the box. They will destroy the seven gates ofthe spillway and also part of the dam and the hydro-electric station. Gatun Lake will then empty itself; the canal will be half drained; thepower will be gone--it will take half a year to repair it all. TheZX-1 can fly up to the east coast, thanks to Zenalishin'sfumbling--yess; but these American fleets are massed in the Pacific;they will have to go around South America to reach the Atlantic--andthat will take weeks. 

"And in that time the Soviet has crossed the Atlantic uncontested andhas paralyzed the heart of America, her eastern states. Ah, it issmagnificent!"

 * * * * *

But Kashtanov's thoughts were elsewhere. Peering hard at the chart, hesaid:

"I have a minute to get clear, eh? Well, I can do that; but won't thewater sweeping through from Gatun Lake after the spillway is wreckedcatch me?"

"No. You run up the hill the spillway channel is cut through; it isshigh ground, and the golf course iss on high ground. No one will seeyou coming or going, naturally, and the box iss not big enough to benoticed at night. The noise of its equalizers will be covered by thewater coming through the spillway. It iss--what they say?--fool-proof. You cannot fail, Kashtanov. And--" he broke into swift-flowing, liquidRussian, his swarthy face lighting up, his arms waving, one of themslapping the other's back. 

"Stop the dramatics, " said Kashtanov, "and speak in English. I'veworked so long in America, Russian is hard to understand. Time tobegin?"

Istafiev glanced at a watch on his wrist. "A few minutes. Look you. "He went to a side locker in the room, opened it, hauled out with bothhands a box of plain dull metal, and put it on the table. It waslarger than the one Chris Travers had seen on the ZX-1, but otherwisesimilar. 

"A double charge of nitro-lanarline iss in this, " murmured Istafievcomplacently. "Imagine it, when released! You know the working well, do you not? Yess. Well, I put it in the plane, ready. " He stepped tothe hut's single door and passed out. Through it Chris could see thetiny clearing, dark under the camouflaged framework, now closed oncemore; the light from the hut showed him the wings of thehelicopter-plane standing there. He heard, moreover, the sound of ashovel from somewhere, and knew that a lonely grave was being dug inthe wilderness. Then Istafiev shouted:

"Grigory! That grave, make it wide, make room for two. " He came backand peered sidewise at Chris. "Not conscious yet?" A foot thudded intothe American's side. "No. Well, I see to him when you are gone, Kashtanov. Yess, thick darkness iss here. Time to begin. Take off yourclothes. "

 * * * * *

Chris was now keenly alert, poised, ready for any chance that mightcome. The odds were two or three to one, and a gun into the bargain, but the stakes were higher than any ever played for before; and astroke had to be made, no matter how seemingly hopeless. Through hislashes he watched, turned things over in his mind--and somethingleaped within him when he saw Kashtanov unbuckle the gun around hiswaist and lay it down, meanwhile taking off the clothes he waswearing: and when he heard the question which followed, and Istafiev'sanswer. 

Naked, lean-muscled and sinewy, Kashtanov paused before the door ofthe cage. "How will this affect me?" he asked. "Painful?"

"You will be conscious of no sensation. You will see me, yess, andthe room, but you will be paralyzed completely while the power is on. "

"Paralyzed, eh?" murmured Kashtanov. "Well, let's go, " and he placedhimself inside the cage. 

Paralyzed, when the power was on! In effect, that left only Istafievin the room: the man Grigory was outside, and the noise of the dynamowould drown any shouts for help. And Kashtanov's gun was on thetable. .. . 

Imperceptibly, Chris's muscles tensed as he judged the distance to thetable and reckoned out each movement after the first leap. Onesweeping blow with the gun would put Istafiev safely out of action;then he could be bound and Grigory summoned and tied also at the pointof the gun. If, by that time, Kashtanov was invisible inside the cage, the levers could be reversed and his body brought back to visibilityand bound. 

Then--a call broadcast from the hut's radio-telephone to headquartersat the Canal and the fleets in the Pacific!

"It'll work, " Chris told himself. "It's damn well got to!"

But a certain part of the invisibility machine did not enter hisplans. 

 * * * * *

The creamy liquid in the glassy dome began, as before, to swirlslowly: but apart from that its action was different. The white mass, instead of discharging the vapor-laden bubbles, became a whipping, highly agitated whirlpool as the tubes below glowed softly and ribbonsof golden light snaked out and laced through the nude body ofKashtanov. The liquid above flowed rapidly in a complete circle, itscenter sucked hollow, exactly as a glass quarter-filled with waterbehaves when rotated quickly. Thus the outer surface of the dome, coated inside with the milky liquid, gleamed and scintillated as thewhirl of light struck it and danced off it: and it even became dimlyreflective. 

In seconds Kashtanov's figure lost definite outline and assumed aghostly transparency that bared the internal organs and veins: andthen his skeleton appeared. 

Istafiev was facing the control panel. As he gathered his limbs forthe decisive leap, Chris's eyes were on his stocky back. But Istafievwas watching keenly the gleaming, glassy dome above. 

He was surveying the action of the white substance and judging thetime of the process by it. Then suddenly his vision centered onsomething that had seemed to move on the surface of the dome. 

Something had moved. Chris, lying against the wall behind, had openedhis eyes fully, had dragged back his legs beneath him and balancedhimself for his leap. And, in distorted perspective, his actions werereflected on the dome. 

Just for a second he poised--then sprang. 

The speed Istafiev showed seemed foreign to the build of his body. Inan instant he had whirled from the switchboard, fingers not lingeringto release Kashtanov, and leaped. 

 * * * * *

They met at the table. Two hands shot out for the gun lying on it. Chris grabbed it first. But he paid for his speed. The swipe he hadaimed with his left arm went wild; a fist thudded into his stomach andbelted the wind from him, and he felt his gun-wrist seized andwrenched back. 

Gasping for breath, dizzy, only the fighting instinct enabled him tocrane a leg behind the other and throw his whole weight forward. Theplanks of the floor shivered under the two bodies that toppled ontothem. 

There was a melee on the floor, furious, savage, mad. In cold fact, itlasted merely for seconds; but Chris was grappling with a man whosestrength was as desperate as his own, and who had not been weakened bya solar plexus blow or a cramping wait of hours in one position: theAmerican had passed through an eternity of physical and mental agonywhen Istafiev, hunching up, strained the finger of his right handupward, searching for the gun trigger. 

One stubby finger found it. Istafiev grunted. The gun trembled fromthe force of the hands disputing its direction; then its ugly snout, stuck out parallel to the floor, and began to creep slowly downwardsas Istafiev bore on it with all his might. 

"So!" he hissed. "It was clever, your little game, but it issfinished!"

But Chris, undermost, had braced his elbow on the floor. The gun held. Every ounce of his strength went into holding that one position, intokeeping the weapon's muzzle away; he was therefore not prepared forIstafiev's sudden strategy. 

There was a quick pull, a tug. Istafiev had wrenched himself over, reversing their positions and dragging Chris uppermost--and, as theAmerican's balance was destroyed, the gun whipped up and fired. 

A bullet sang past his head. It missed by inches. But from behind camea sound as of rending cloth. The glassy dome above the cage of themachine had splintered into countless fragments. 

The effect was amazing. The shafts of light from the machine's tubeceased; creamy liquid dribbled out from the cracked dome, and, as itmet the air, frothed into billows of dense gray smoke. In seconds, theroom was choked with a thick, foggy vapor that obscured every objectin it as well as the blackest of moonless nights. 

 * * * * *

Istafiev had not fired again, could not. With a quick, frantic wrenchand twist Chris had knocked the gun from his hand, and it hadslithered away, now lost in the bunching smoke. But Istafiev's otherhand, steel-ribbed with tense muscles, had darted like a snake intothe American's throat, and under that iron, relentless grip Chris wasweakening. His head was whirling; the old wound throbbing waves ofnausea through him. Desperately he tried to struggle loose, flailingwith his legs--but useless. He knew he was slipping; slipping. .. . 

Then, out of the gray, all-hiding mist, came a voice. 

"Istafiev! Where are you? Call! The machine's broken; I'm out andinvisible. Where is the American?"

Kashtanov!

Istafiev hissed:

"It iss all right. He will be finished in a moment. But you--go! Thebox iss aboard the plane; don't wait! You must not take chance ofbeing hurt. Go to your work. Call Grigory in. Go, Kashtanov!"

"I go, Istafiev. "

"No, you don't!" Chris Travers croaked almost inaudibly. "_Youdon't!_"

Thought of the Canal lying there defenseless, of Kashtanov speedingtowards it on his wrecker's errand, kindled within him a strength thatwas unnatural, superhuman. Like a wildcat he tore loose from thechoking grip on his throat; Istafiev tried to subdue that sudden, unlooked-for surge of power, but could not. Five piston-like, jabbingblows crunched into him from Chris's hurtling fist, and with the fifthIstafiev faded quietly out of the picture. .. . 

Chris sprang up and started a leap for the door he could not see. Abody brushed against him; dimly through the smoke he saw the mancalled Grigory, and Grigory saw him, but not for long. A whaling swinglifted him two inches clear of the floor, and then he went down ontothe peacefully recumbent Istafiev; and Chris Travers, fighting mad, stormed from the hut into the clearing outside. 

The camouflaged framework had been raised; soft motors were purringhelicopter propellers around and lifting a plane up towards the starshanging high above. 

The airplane was already feet off the ground and sweeping straight up. A sane man wouldn't have thought of it, but Chris wasn't quite sanejust then. With a short sprint, he launched himself into a flyingleap, grabbed out desperately--and felt the bar of the undercarriagebetween his hands. 

The plane jolted. Then it steadied; rose with terrific acceleration. And Chris hauled himself up onto the undercarriage and clung to one ofthe wheel-stanchions, breathing, hard, hidden by the fuselage from theinvisible pilot. 

The clearing and the hut, with smoke billowing from it, dropped intonothingness. The night enclosed the helicopter-plane. 

 * * * * *

From the air, Panama Canal at night is a necklace of lights strungacross the thin neck of land that separates sea from sea. Then, as ahigh-flying plane drops lower, the beams of light loosen into widelyseparated patches, which are the locks; between them the silky blackribbon of water runs, now widening into a dim, hill-girt lake, nownarrowing as it passes through massive Culebra Cut, then wideningagain as it comes to the artificial Gatun Lake, at the far end ofwhich stands Gatun Dam and its spillway. 

Silence hung close over the Canal. The last ship had passed through;the planes that daily maneuver over it had returned to their hangars;the men who shepherd ships through the locks had gone either to bed orto Panama City or Colon. The Canal, as always at night, seemed almostdeserted. 

To Chris, clutching tight to his hazardous perch, it looked utterlydeserted. The ride had been nightmare-like, fraught every second withperil. Several times the whip of wind had come near tearing him loose;the cold air of the upper layers had numbed his fingers, his wholebody; he was chilled and, experiencing the inevitable let-down whichcomes after a great effort, miserable. Just then, the task aheadappeared well-nigh impossible. 

The only thing in his favor was that Kashtanov apparently did not knowhe was aboard, since the plane had flown evenly, steadily, not tryingto shake off the man hanging to its landing gear by somersaulting inthe sky. Evidently the jolt as it was rising hadn't warned the unseenpilot; the fog from the broken machine had obscured Chris's wild leap. 

But what, he thought, of that? The element of surprise was in hisfavor--but how to gain advantage by it? He had no weapon, nothing savebare hands with which to subdue a foe as elusive as the wind that wasnow hurtling by him. Clinging there, slipping now and again, drenchedwith cold, the odds looked hopeless. 

Then, suddenly, the booming of the main motor stopped. Only a quietpurring from the wings took its place. The helicopter-plane hoveredalmost motionless, quiet and deadly like a sinister bird of prey. Itbegan to drop straight down through the dark. Chris Travers glancedbelow. 

 * * * * *

There, misty, fainty, small as the toy of a child, lay Gatun Dam, withthe spillway in its center. 

Chris stared. So small the dam looked--this dream of an engineer, thistiny outpost of man's genius thrust boldly into the breast of thetropics, holding back a whole lake with its cement flanks, enablingocean to be linked to ocean! It was the heart of the Canal; if burst, the veins would be drained. 

Something that cannot be caught in words seemed seize the loneAmerican then. As in a trance, he saw more than the dam; he saw whatit symbolized. He saw the Frenchmen who had tried to thrust the Canalthrough first, and who had failed, dying in hundreds. He saw the menof his own race who had carried that mighty work on; saw them gougingthrough the raw earth and moving mountains, tiny figures doing thework of giants; saw them stricken down by fever and disease, sawothers fill the empty files and go on, never wavering. He saw themcomplete it and seal the waters in captivity with the dam that laybelow. .. . 

And with that vision of stupendous achievement, cold, weariness, hopelessness passed from Chris Travers and swept clean away. The oddsthat had loomed so large fell into insignificance. 

The golf course spread out and became dimly visible as the planedropped cautiously down. Away to the left there were the few twinklinglights of Gatun Dam, whitening the crests of the waters that tumbledthrough the spillway. Their drone was dully audible. On every otherside dark rolling hills stretched, covered in untamed jungle growth. The golf course was shrouded by them. Its smooth sward made a perfectlanding place; an ordinary plane might alight there. 

Lower, lower, ever so slowly. A bare one hundred feet, now. Chrisscanned the lay of the land. Right close to the spot Kashtanov hadchosen to set the plane down on was a deep sand-trap, put there tosnare unskilful golfers. Chris steadied himself on the cross-bar. 

"I'll have to go up over the side and grab him, " he planned. "Thenhold on to his throat till I feel him go limp. "

The wheels of the plane touched gently, and she settled to rest. 

 * * * * *

In one furious movement Chris was off and springing up the side of thefuselage into the single cockpit, his hands clutching for theinvisible man who sat there. 

He heard a croak of alarm; then his fingers thumbed into bare fleshand slid up over a nude shoulder to the throat. They tightened, boredin, held with terrible pressure. Sprawled over the cockpit, he clunggrimly, to what seemed nothing more than air. 

Spattering noises came from somewhere. An unseen body thrashedfrantically. Transparent hands clawed over the American's frame, worried at him. But he held his grip, tightening it each second. Therewas a gasping, choking sound, a desperate writhe, another scratchingof the invisible hands--and then came what Chris had feared, what hecould not guard against since his eyes could not forewarn him. A heavymonkey-wrench appeared to rise of its own accord from the floor of thecockpit and come swinging at his head. 

He ducked at the last second. But it clipped him; his brain whirleddizzily. The next moment he slithered off the plane and fell to theground, dragging the unseen Kashtanov with him. And as he pitched intothe damp grass, the shock dislodged his grip. 

He was up in a flash, but the damage was done. The monkey-wrenchcurved through the darkness in a vicious swipe that landed it flushagainst his jaw; swung back, pounded again like a trip-hammer--againand again and again. .. . 

Chris reeled back, teetered on the edge of nothingness, then wenttumbling crazily down into the sand-trap behind. One leg was doubledunderneath him as he crashed. 

A voice floated down out of the darkness. "That is the end of you!" itsaid. But Chris Travers did not hear it. .. . 

 * * * * *

Pain. Agonizing pain. The whole lower side of his face was a burning, throbbing, aching lump of flesh, and his left leg seemed on fire. Whathad happened? Where was he?

Then came remembrance, and it was far worse than the fangs of painthat were gnawing him. Chris cried out--a cracked, twisted cry. Kashtanov, the dam--the box of the ray! How much time had passed?

He hunched his body over and stared up. Limned against the starlightwere the wings of a plane, still standing where it had landed besidethe sand-trap. He clutched his thoughts. The plane meant--it meantKashtanov had gone on his errand, had not yet returned? Only minuteshad gone by since the blows from the monkey-wrench. But was the boxplaced yet? Was Kashtanov already hurrying back?

He listened. From far away came a drone that was separate from thethrobbing of his head. The drone of waters, controlled waters. Thenormal sound of the spillway of Gatun Dam. The box had not yetunleashed its disintegrating bolt of blue. 

"I've got to stop it!" he whispered. 

He tried to rise. Only one leg held. The other twisted awrily with arasp of broken bones. A spearing pain tore through him. Useless! Hisfall had broken it. He could not rise, could not walk, much less run. He was no more than a cripple. 

"Oh, God!" he groaned, "How can I, how can I?"

Then his eyes fell on the plane resting above him. 

"I've got one leg, " he muttered, "and two hands and two eyes. .. . They're left me. Yes!"

He rolled over. He shoved with his right leg and clawed at the bank ofthe sand-trap. Inch by inch he wormed up, slipping, scraping. The sandgrated into his battered face and seeped through onto his tongue; hecoughed and spluttered, groaning from the effort and his feebleness. Spots of blood showed black against the crazy course he left behindhim; ages seemed to pass before he thrust his head over the top of thebank, dug his chin into it and pulled onto level ground. Ages, but inreality only seconds, and the whole Canal--America--lying at the mercyof what each one of those seconds might unloose!

 * * * * *

But the plane was near now, and it almost seemed that some unseenforce mightier than the strength of men hauled Chris's broken body toit and up the stretch of its fuselage-side into the cockpit. 

Ordinarily, he should have been delirious from the pain of jaw andleg, but the controls of the plane were before him and he saw nothingelse. Wings and propeller were better than legs! He was in hiselement: by the sixth sense of born airmen, he knew and could handleany flying machine, no matter how foreign. 

In a second, his fingers had fumbled onto the starting button. Thechoke of the motor and then its full-throated roar were sweet to hisears. 

The lonely golf course and the night re-echoed with the bellow oftwelve pistons thrusting in line; watching, one would not have dreamedthat a cripple was at the controls of the plane that now swung aroundwith a blast of power, leveled its nose down the course and racedsmoothly over close-clipped grass. Its wheels bumped, spun on theground and lifted into air. 

A mile to the dam! Istafiev's words came back to him. It would takeKashtanov twenty minutes at least, for he would go cautiously. But howlong had passed--how long? That was the agonizing question. 

Staring forward through the hurtling prop, the night rushed at him;the dark hills melted away to either side; clear ground swept intoview and then a long black thread that was the spillway channel. Behind was the bubbling, leaping flow of the spillway itself, andGatun Dam. The smooth cement sides were as yet unharmed. 

"Thank God!" Chris muttered. "Now, where--where?"

A stream of light flowed out from the hydro-electric station on theleft side of the spillway channel. The opposite bank was bare, runningright up to the face of the dam beneath the spillway's seven gates. There the box was to be placed. But from the air, the light wasuncertain, deceptive--and a little two-foot-square box was all he hadto go by!

"I can't see!" Chris said hoarsely. "I can't see!"

 * * * * *

Like a roaring black meteor the plane hurtled over the banks of thespillway, the eyes of its pilot scouring the ground. It zoomed just intime to miss the wall of the dam, banked, doubled like a scaredjack-rabbit, dove down again, coming within feet of the spillwaychannel. Mad, inspired flying! But what good could it do?

Then from its cockpit came a yell. 

"There! There! By heaven, I can make it!"

Two or three hundred feet--it was not clear just how far--from theface of the dam, on the bare right bank of the channel, a tinypin-prick of black was moving slowly along. It seemed to move byitself through the air. And now, as the screaming plane banked againand came rushing closer, the pin-prick grew into a black box thatsuddenly stopped its advance, held motionless some four feet off theground. Though the man who held it was not visible, Chris could fancyhim staring up at the plane, could fancy the look of consternation onhis unseen face. 

Two hundred feet was the range of the rays! Was Kashtanov that close?Obviously the controls had not yet been set, for he still held thebox. But he could switch them on in a second and fling the deadlymachine up toward the dam, if he were at present just out of range. Asecond--a second!

"Damn you, here goes!" roared Chris. 

He wrenched the stick way over. The plane appeared to hang crazily onone wing. Then it leveled off and stuck its nose down, flipping itstail up, and down--down--down it bellowed; with no hope in the worldof ever coming out of its insane plunge. 

What he saw in that last momentary glimpse was burned forever intoChris Travers' memory. There was the black box, hanging in the airstraight before the plane's thundering nose; there, behind it, theblack tide of the spillway waters; and, still further behind, he couldsee the other bank and the hydro-electric station, and a few tinyfigures that rushed out from it just then to see what some fool flyerwas doing. 

All this flashed into his sight, etched against the sable night as ifin flame. Then the plane's snout smashed into the black box hangingbefore it, and the propeller crunched through a naked, invisible body. A ragged scream that marked the passing of Kashtanov split through theair for a flash of time, and the dark, blurred mass that was anairplane teetered clean over and flopped into the rushing spillwaychannel. 

 * * * * *

The men who had scrambled out from the hydro-electric station staredat each other blankly. One of them stuttered:

"But--he did that deliberately! Nothing went wrong with his ship! Isaw him! He seemed to be diving at something!"

"Come on!" snapped another. "We might be able to get him out. A madfool like that's just the kind who'll live through it. "

 * * * * *