Foster scowled as he lit a cigarette and stared through the gloom at the violet-lighted tent from which the disturbing sound still came. Seven days of experience with Layroh's peculiarities had begun to make them a little irritating. His sternly enforced code of rules was simple enough. Never approach Layroh unless called. Never touch Layroh's instruments. Never approach Layroh's tent. Never ask questions. Layroh neither ate with the men nor mingled with them in any way that could possibly be avoided. As soon as they made camp each night he set up his small black tent and remained inside it until camp was broken the next morning. No one knew whether the man ever slept. All night long the violet light glowed inside the black tent. The men had wondered about the unusual color of that light, then had finally decided it was probably something required by the same eye weakness that made Layroh wear heavily smoked goggles, both day and night. Strange sounds in the night as Layroh worked with his apparatus in the black tent were nothing unusual, but to-night was the first time that Foster had ever heard this peculiar whining buzz. As he listened it rose in a sudden thin crescendo that rippled along his spine like a file rasping over naked nerve-ends. For one shuddering second there seemed to be an intangible _living_ quality in that metallic drone, as though some nameless creature sang in horrible exultance. Then abruptly the sound ceased. * * * * * Foster drew a deep breath of relief and ground his cigarette into the sand beside him. Better try to get to sleep again before Layroh started some new disturbance with his infernal apparatus. He was just settling down into his blankets when a movement in the tent drew his attention back to it. Layroh was apparently changing the position of the violet light, for his tall figure was suddenly silhouetted against the tent wall in sharp relief. Foster started in surprise as another figure loomed darkly beside that of Layroh. For a moment he thought that the unprecedented had happened and some member of the expedition was inside those jealously guarded tent walls with Layroh. Then he saw that the figure must be a mere trick of the shadows cast by the moving light upon some piece of luggage. It looked like the torso of a man, but the head was a shapeless blob and the arms were nothing more than boneless dangling flaps. A moment later the light moved on and both shadows vanished. Foster grinned sheepishly over the momentary start the distorted shadow had given him, and determinedly rolled himself in his blankets to sleep. It was after sunrise when he awoke. The rest of the camp was already up, but there was one member of the party missing.