He flew low as he circled back. They had traveled far on their journey below ground; it was even a longer route where he and Towahg had circled about. But it was the only route he knew; he could take no chances on a short-cut and a possible long-drawn search for the little valley. He followed the trail. The quick dusk was near; but in an hour's slow flying, while his eyes searched the hills and hollows, the valley was in sight. He came down slowly in a black sky, with only the soft, muffled roar of the lower exhausts. It was growing dark, and he leaned from an open door to see more clearly his position. All was different from the air, and he needed time and careful scrutiny to get the bearings of the place. The soft thunder from below was in his ears when a sound pierced through. His own name! And it was Diane's voice calling him in a terrified tone. "Walter!" she cried. "Help! Help! Oh, Walter, come quickly!" * * * * * The scene below was lighted by fitful fires. He was above the upper valley, a hundred yards from their cave: his mind was oriented in an instant, and he knew each foot of ground. And here, where neither Diane nor Chet should be, was Diane. He saw her running in the bright glare of his landing light that he now switched on; saw a black shape hurl itself upon her; she was struggling. He threw himself back at the controls to send the ship like a thunderbolt upon the earth. A pistol was in his hand as he leaped from the still-rocking ship and threw himself upon the thing that ran and tried to carry a struggling burden in its arms. He could not fire; but he brought the pistol down upon a heavy skull. The hairy figure seemed never to feel the blow. It dropped the body of Diane and turned, and its slavering, shining fangs were set in a horrible face that Harkness recognized. It was the leader of the tribe, and he had dared to attack. But where was Chet? What of his arrows and their detonite tips? These thoughts were crowding through his mind in the instant that ape-like fingers gripped at his throat--the instant while he was bringing the pistol forward and up. A light charge of detonite in pistol ammunition--but no living body could withstand the shock. Harkness leaped over the fallen foe to reach the girl. She was half risen to a sitting posture as he came. "_Dieu!_" she was whispering; "_Ah, le bon Dieu!_" Then she cried out: "Walter! Oh, Walter, they have killed Chet! Down there!" Her hand was pointing. She grasped at Harkness' hand to draw herself to her feet and race with him toward the cave. * * * * * "Just at dark," she explained gaspingly as they ran. "It was their chief, and there were others with him. They leaped upon Chet--before he could reach for his bow. They had seemed so friendly after you left--but they were short of food--" Her voice was sobbing now, but she kept on, and she set a pace that Harkness could not outdistance.