A tree stood near and the silk cord was soon fastened. Carnes disappeared over the cliff and in a few moments Dr. Bird slid down the cord to join him. He found the detective seated in the crotch of a tree only a few feet from the face of the cliff. From the cliff came a pronounced murmur of voices. Dr. Bird drew in his breath in excitement and moved forward along the branch. He touched the stone and after a moment of searching he cautiously raised one corner of a painted canvas flap and peered into the cliff. He watched for a few seconds and then slid back and silently pulled Carnes toward him. * * * * * Together the two men made their way toward the cliff and Dr. Bird raised the corner of the flap and they peered into the hill. Before them was a cave fitted up as a cross between a laboratory and a hospital. Almost directly opposite them and at the left of a door in the farther wall was a ray machine of some sort. It was a puzzle to Carnes, and even Dr. Bird, although he could grasp the principle at a glance, was at a loss to divine its use. From a set of coils attached to a generator was connected a tube of the Crookes tube type with the rays from it gathered and thrown by a parabolic reflector onto the space where a man's head would rest when he was seated in a white metal chair with rubber insulated feet, which stood beneath it. An operating table occupied the other side of the room while a gas cylinder and other common hospital apparatus stood around ready for use. Seated at a table which occupied the center of the room were three men. The sound of their voices rose from an indistinct murmur to audibility as the flap was raised and the watchers could readily understand their words. Two of them sat with their faces toward the main entrance and the third man faced them. Carnes bit his lip as he looked at the man at the head of the table. He was twisted and misshapen in body, a grotesque dwarf with a hunched back, not over four feet in height. His massive head, sunken between his hunched shoulders, showed a tremendous dome of cranium and a brow wider and even higher than Dr. Bird's. The rest of his face was lined and drawn as though by years of acute suffering. Sharp black eyes glared brightly from deep sunk caverns. The dwarf was entirely bald; even the bushy eyebrows which would be expected from his face, were missing. * * * * * "They ought to be getting back," said the dwarf sharply. "If they get back at all," said one of the two figures facing him. "What do you mean?" growled the dwarf, his eyes glittering ominously. "They'll return all right; they know they'd better."