"Search beams?" Hilary echoed inquiringly. "Yes. They act like X-rays, more powerful though, and with the further property of rendering everything they touch transparently crystal for depths of ten to fifteen feet. Lead is the only element they can not penetrate. Another secret our scientists can not fathom, so they talk learnedly about the stream of rays polarizing the structure of matter along a uniaxis." "Can't those lenses be duplicated, and turned as weapons against the Mercutians?" "No. They are made of a peculiar vitreous material native to Mercury." "And no one has found out the principle on which they work?" "Well, there have been theories. We haven't many scientists left, you know. But the most popular one is that these lenses have the power of concentrating the rays of the sun to an almost infinite degree, and then spreading them out again, each individual beam with the concentrated energy of the whole. Some new way of rearranging quanta of energy." "Hmm!" Hilary's brow was wrinkled. For a long moment he stared and thought. * * * * * At last he snapped back to their present situation: the dead guard at their feet, the dismembered body of Amos Peabody, the cowed groups of Earthmen on the speeding conveyors, keeping respectful distances. "We'd better start moving if we want to get away," he said. "It's no use." Grim spread his hands resignedly. "We'll have to take our medicine." Hilary flared angrily. "You're talking nonsense. What's to prevent us from hopping to another platform? There is no other Mercutian in sight." "No, but there were plenty of Earthmen who saw us." "They won't tell." "Oh, won't they?" Grim shook his head quietly. "You don't realize what has happened. Their spirit has been crushed until they are actually slavish in soul as well as in body. They fought bravely enough on the first invasion. Even after the conquest there were plenty of men looking for an opportunity to fight them again. Amos Peabody headed the revolt. It was smothered in blood, so effectually that only slaves are left. Peabody was left as a horrible warning. He was sent from city to city to be exhibited to the populace, unattended on the way, so confident were the Mercutians of the terror they had inspired." "So you think those Earthmen who saw us will report to their masters," Hilary said slowly. Grim nodded. "I know it--they'll expect to curry favor in return." Hilary felt a web of circumstance tighten around him. His jaw tautened. Thank the Lord he had been away--on his own. He had not the soul of a slave--yet. "Won't you fight for your life?" he asked the big man curiously. A spark lit in the mild blue eyes, died down. "Yes if there were a chance," he said dully. "But there is none. The whole Earth is honeycombed with their guards. They have fliers, sun weapons, invisible search beams. We'd never elude them."