He wondered, as he went, who in the devil was behind it all. The radium-finding project had been kept strictly secret. Not another soul was supposed to know of the earth-borer and its daring mission into the heart of the earth. Yet, obviously, someone had found out, and whoever it was had laid at least part of his scheme cunningly. An old man and a girl cannot offer much resistance: he, Phil, would have been well taken care of had it not been for the water jug. So far, there were at least two in the plot: the man who had ambushed him and the unknown who had evidently kidnapped both Professor and Sue Guinness. But there might be still more. There might be friends, nearby, of the man he was tracking. The fellow might have reached them, and warned them that the scheme hadn't gone through, that Phil was loose. They could very easily conceal themselves alongside their partner's tracks and train their rifles on the tracker.... The trail was leading up into one of the cañons in the cluster of hills to the west. For some distance he followed it up through a slash of black below the steep moonlit heights of the hills to each side--and then, suddenly, he vaguely made out the forms of two huts just ahead. Immediately he stooped low, and went skirting widely off up one side. He proceeded slowly, with great caution, his rifle at the ready. At any moment, he knew, the hush might be split by the cracks of waylaying guns. Warily he advanced along the narrow cañon wall above the huts. No lights were lit, and the place seemed unoccupied. He was debating what to do next when his attention was attracted to a large dark object lying in the cañon trail some twenty yards from the nearest hut. Straining his eyes in the inadequate moonlight, he saw that it was the outstretched figure of a man. His quarry--his ambusher! * * * * * Phil dropped flat, fearful of being seen. Keeping as best he could in the shadows, fearing every moment to hear the sharp bark of a gun, he crawled forward. It took him a long time to approach the sprawled figure, but he wasn't taking chances. When within twenty feet, he rose suddenly and darted forward to the man's side. His rapid glance showed him that the fellow was completely out: and another quick look around failed to show that anyone else was watching, so he returned to his examination of the man. It was the ambusher, all right: a Mexican. He was still breathing, though his face was drawn and white from the loss of blood from a wound under the blood-soaked clothing near his upper right arm. A hasty search showed that he no longer had his gun, so Phil, satisfied that he was powerless for some time to come, cautiously wormed his way towards the two shacks.