"They're bombing the base now," she reported dully. "We've been able to miss being hit by keeping a cover of volunteers up to attract the seeking units before they reach us. And the Aliens are within three million miles. We can't hold out much longer." "Don't forget your optimism," he said. He'd meant it for reassurance, but she stared back as if he'd slapped her. "I mean your computer calculations on victory for Earth. How come they moved in so quickly?" "It's been three days," she told him. "Don't you know how long you've been out there?" He hadn't kept track. The cluck of the computer ending its work interrupted them, and she held the results up to the screen for him to copy with the camera at his end. He studied the formulae for long, wasted minutes before he could accept them. Then he went on to other work. There was no shield possible for any object bigger than about twice the size of the cage they had used. There could never be any way to protect a man from the Aliens. It was to be a death watch he kept, apparently. And Pat must have known it when she saw the formulae, since she had picked up sufficient basic knowledge to read it. He stood staring up at the space above him, letting the hate harden inside him, while he pictured the base in the hands of the invaders! Humans were beyond saving, according to the figures he had now. But it was still not too late for vengeance. This time he deliberately sought for a taboo in his mind to discourage thought along hindering lines. The forbidden topic was the question of why the Aliens had to exterminate life as they advanced. He wrestled with it briefly, rejoicing in the knowledge that he seemed to be gaining ease in overcoming the compulsory behavior which had been imposed on him. Life must be poison to the Aliens! Probably it was for that reason that they had been able to detect it in the first place. And they could never rest until it was wiped out to the last living cell. He glanced at his formulae again, and nodded. If their existence were somehow based on the breakdown of radio-active isotopes, and if protoplasmic life slowed up that process, then they _had_ to exterminate it. How? He asked it automatically, remembering the force they used to sterilize space before them. And that had an answer, too. Even protoplasmic life apparently needed a tiny, incredibly small amount of radioactivity to function. Blast enough of the raw life-force against it, and all nuclear breakdown would stop--and with the stopping of that, there would be no life. It was logical that the weapon of the Aliens should be the one thing which they themselves feared most. Tiny--incredibly weak--as the energy of those life forces were, they could do more in their inhibiting of the great force of nuclear readjustment than ten million atomic bombs!