Troy Gordon's personal living quarters were on the lowest of the station's three underground levels, behind the central power plant and utilities section. Considerable privacy was their only attraction; and since the arrangement kept Troy, during his off-duty hours, close to his responsibilities as the station's maintenance engineer, neither Dr. Clingman nor the Hammerheads had objected to it. He was a useful man; and to the useful, minor privileges could be extended. Troy had been able to take advantage of that circumstance. The room in which Newland was hidden lay behind his own quarters, forming an extension to them. The entrance to it was concealed, and while a careful search should have disclosed it, Troy--so far as he knew--had as yet given no one a reason to initiate such a search. The back room was not part of the station's original design; he had cut it secretly out of the rock. With the equipment at his disposal, it had been a relatively minor job. But it involved a very ugly risk. Discovery would have meant death, and no easy one. With the exception of the cooperating chief scientists, the Hammerheads' attitude towards their captives was largely one of watchful indifference, so long as no one got out of line. But they had taken one measure which insured that, after a short time, there was very little inclination left among the prisoners to get out of line knowingly. At intervals of about a month, whether or not an overt offense had been committed, one more member of Earth's Cassa Expedition was methodically tortured to death by the aliens; and a group of his fellows, selected apparently at random, was obliged to witness the matter while fastened to a device which allowed them to experience the victim's sensations in modified form. Troy had been included twice in the observing group. He hadn't known whether it implied a personal warning or not. In the Hammerheads' eyes, he was a useful servant; it might be that he was also a suspected one. Nevertheless, it had been necessary to construct the back room. One day, he was returning through the desert from one of the outlying automatic stations under his care when he caught the momentary whisper of a distress signal in his groundcar's receiver. The slight sound had put his hair on end. It was an Earth signal, on an Earth band; and with the _Atlas_ off-planet it could have only one possible source. In seconds, it wavered out and was lost, but Troy already had established the direction. * * * * *