He gripped his consciousness hard. It was like a delirium: he was lying sprawled beside the seat, twisted round so that he saw, hanging in the cubby's entrance door, an automatic, dribbling a wisp of smoke--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 was throbbing his brain dizzily, but he realized that the service repeater he 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 a voice, speaking very softly and with a slight thickness of accent. "Do not move," it said. "I fire if you do. Now, listen: What did you do 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 deal with. For with humans, strategy can be used.... * * * * * He groaned. He saw plainly that the unseen marauder had been aboard when he had thrown the box over, and thus had not seen it explode in midair: did not know whether it had been tossed out or merely rendered harmless by being tampered with. If only the latter, it could be quickly repaired and set again. That must be the invisible man's reasoning. 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 felt a thrill when he saw the automatic come forward through the air, descend, and pause right next to his head. He sensed a man close behind 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 man to turn his head. His legs braced imperceptibly. And then: "Like hell!" roared Chris Travers, and shot his whole weight backwards, grasping the service gun, whipping it around and yanking the trigger three times at the same instant. Shooting at nothing! But, even above the bunched roar of the explosions, there pierced out a howl of agony that died quickly to a sobbing moan. Chris saw the automatic drop to the floor, felt the invisible 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 heavily towards the cubby's door, towards the ladder that led up to the fore-and-aft cat-walk.