There was no use in reminding Miles that he'd tried to warn him. Earth hadn't been able to heed such warnings. He handed the papers back, his mind tormented by a picture of seven hundred men--men probably like the guards who'd called him all right--who had lost their marginal chance to live because a robot had failed. It was nonsense, his mind told him. Soldiers were meant to die. But the picture remained. "So what happens to me now?" he asked. "You'll try again, of course," Miles answered, apparently surprised at the question. "At least the fact that they worked that hard to eliminate the ships with the screen indicates you're on the right track." Norden stared at him despairfully. "It's like tracing a single drop of water in the ocean--or looking for a trace of life that can be detected for millions of miles when you're in the middle of hordes of living creatures. I've been working on that already. And the only reason we _could_ detect and screen the lizard signals was because they were unique. "Hardwick was right about that, too. You have to look for life forces where they're scarce. I need isolation from people, animals--even from germs and viruses, probably." Pat gestured to a map on the wall. "There are the mine installations on the other side of the Moon. Would they do?" He had no idea, but it was the best he could hope for. He nodded slowly, and she turned towards the door. "Then what are we waiting for?" she asked. "We've got too little time now." "You're not going, Pat," he told her. "Nobody is. I need isolation from life, remember! Besides, if there's any means of communication between here and there, I'll need you here to work the communicator." There was a television link that was still useful, as a quick check showed. And there were ships to carry as much equipment as he needed, including two rabbits, and a male and female sand lizard in little airtight cages where oxygen could be supplied from tanks. He had no idea of what he might need, and had to take everything he could imagine as being useful. VI Three hours later, he stood alone in the building that had served as a barracks for a mine crew. He watched the rockets leave, and began opening the airlocks to space. Any bacteria left by the former men would quickly perish, he felt sure. But he had to be thorough. He had no hope of success yet. He might be keeping a death watch over the human race as the Aliens moved in--or a life watch, since he was seeking life while they were intent on ending it. But he, at least, was no living thing, and the life detectors of the Aliens should miss him. Somehow, he'd learn enough to seek vengeance among them. They'd made a mistake in creating him with all the ability of the original William Norden, and the thinking speed of a robot. They'd made a bigger mistake in assuming that a robot was only a robot, and that orders in the form of compulsions would be followed without question.