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 thi
s 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.
* *