Chris's nerves were raw and his face sopping with sweat beneath its mask when suddenly he stopped at sight of something that lay on the cat-walk, with the main fuel tanks on the girders just above it and the entrance to the control car just below. * * * * * It was a black box, perhaps two feet square and a foot in depth, made of dull metal that did not reflect the rays of the light bulb placed at the head of the ladder leading down in the control car. There were three curious little dials on its face, and the trembling finger of each one was mounting. It had been strategically placed. An explosion at that point would rip open the fuel tanks, split the largest gas bag, wreak havoc on an intricate cluster of main girders, and destroy the control car with its mechanism. "No wonder the ZX-2 crashed!" Chris muttered. Then his hands swept down. The next instant he was hugging the thing tight to his chest and stumbling down into the control car, hearing only a high-pitched, impatient whine that was coming from the box as the 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, strangled by gas, stirred slightly. The gray-haired commander was stretched there, one arm limply rolling as his ship, which had gone so suddenly from him, rolled. Subordinate officers were tumbled around him. Death rode the control car. But down to it and through it now came one who was alive, a figure made grotesque by the mask it wore and the pack of the parachute strapped to it, who threaded past the littered bodies, an ever-rising whine wailing from the box clasped in his arms. With a leap, he was at one of the car's port-holes, fingers fumbling at the heavy bolts. The seconds seemed eternal, and the box's whine had become a shattering, sinister scream when at last the bolts loosened. The round pane of glass teetered back, swung open--and the masked man slung his metal burden out, out from the ZX-1 into the gulf between sea and sky. It arced through the sunlight, went spinning down, became a dot, its screaming faded. Then something synchronized within it, and it was gone--in a burst of weird, bluish light, whose fangs forked upwards for a second, their unearthly flash dimming even the sunlight, and then were gone, too.... * * * * * Chris found that his whole body was shaking. For a moment he stood there 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 came back 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!"