He turned and went into the darkness after the water party. He followed them down to the fork, and it was quite easy then to slip aside among the tumbled rock and leave them, working his way slowly and silently downstream. After several days in the dimness of the cave, he found that the star-shine gave him light enough to move by. It was hard going, even so, and by the time he reached the approximate place where Saul had tried to kill him he was bruised and cut and considerably shaken. But he picked his spot carefully, crossed the stream, and began to search. The chill deepened. The rocks that had been hot under his hands turned cold, and the frost-rime settled lightly on them, and Trevor shivered and swore and scrambled, fighting the numbness out of his body, praying that none of the loose rubble would fall on him and crush him. He had prospected on Mercury for a long time. Otherwise he would not have lived. * * * * * He found it more easily than he could have done by day, without a detector. He saw the cold pale light of it gleaming, down among the dark broken rock where Saul had thrown it. He picked it up. He dandled the thing in his palm, touching it with loving finger tips. It had a certain cold repellent beauty, glimmering in the darkness--a freakish by-product of Mercury's birth-pangs, unique in the Solar System. Its radioactivity was a type and potency harmless to living tissue, and its wonderful sensitivity had made it possible for physicists to explore at least a little into those unknown regions above the first octave. In a gesture motivated by pure curiosity he lifted the stone and pressed it tight against the flesh between his brows. Probably it wouldn't work this way. Probably it had to be set deep into the bone.... _It worked, oh God, it worked, and something had him, something caught him by the naked brain and would not let him go._ Trevor screamed. The thin small sound was lost in the empty dark, and he tried again, but no sound would come. Something had forbidden him to scream. Something was in there, opening out the leaves of his brain like the pages of a child's book, and it wasn't a hawk, or a Korin. It wasn't anything human or animal that he had ever known before. It was something still and lonely and remote, as alien as the mountain peaks that towered upward to the stars, and as strong, and as utterly without mercy. Trevor's body became convulsed. Every physical instinct was driving him to run, to escape, and he could not. In his throat now there was a queer wailing whimper. He tried to drop the sun-stone. He was forbidden. Rage began to come on the heels of horror, a blind protest against the indecent invasion of his most private mind. The whimpering rose to a sort of catlike squall, an eerie and quite insane sound in the narrow gorge, and he clawed with his free hand at the one that held the sun-stone, tight against his brows. He tore it loose.