"The Hairy People were the rulers," he went on, "and the Furry Ones were their slaves. In the revolt that eventually split Lomihi into two warring races this city, Aryk, was destroyed by a strange vegetable blight and the ancient knowledge was lost to both races." "But," Rolf frowned thoughtfully, "what keeps Lomihi from crashing into the island? Surely the two columns at either end cannot support it?" "The island is the answer," said Tanner. "Somehow it blocks the force of gravity--shields Lomihi from...." He caught his breath suddenly. "The outlaws!" he cried. "They're after Altha." Rolf caught a glimpse of a sleek rocket flyer diving upon Altha's frail wing. He saw the girl go gliding steeply down toward a ragged jumble of volcanic spurs and pits and disappear from view. He turned to see the old man pushing another crudely constructed glider toward the outer wall of the rock chamber. Tanner tugged at a silvery metal bar inset into the stone wall. A section of the wall swung slowly inward. Rolf sprang to his side. "Let me follow," he said. "I can fly a glider, and I have my expoder." The older man's eyes were hot. He jerked at Rolf's hands and then suddenly thought better of it. "You're right," he agreed. "Help her if you can. Your weapon is our only hope now." Rolf pushed up and outward with all the strength of his weary muscles. The glider knifed forward with that first swift impetus, and drove out over the Barrier. The Furry Ones were struggling insect shapes below him, and he saw with a thrill that larger bodied warriors, whose bodies glinted with a dull bronze, were attacking them from the burnt-out wastelands. The Hairy People had come to battle the invaders. He guided the frail wing toward the shattered badlands where the girl had taken shelter, noting as he did so that the rocket flyer had landed near its center in a narrow strip of rocky gulch. A sudden thought made him grin. He drove directly toward the grounded ship. With this rocket flyer he could escape from Lomihi, return through the thirty-seven caverns to the upper world, and give to thirsty Mars the gift of limitless water again. * * * * * A man stood on guard just outside the flyer's oval door. Rolf lined up his expoder and his jaw tensed. He guided the tiny soarer closer with one hand. If he could crash the glider into the guard, well and good. There would be no explosion of expoder needles to warn the fellow's comrades. But if the outlaw saw him Rolf knew that he would be the first to fire--his was the element of surprise. A score of feet lay between them, and suddenly the outlaw whirled about. Rolf pressed the firing button; the expoder clicked over once and the trimmer key jammed, and the doughy-faced Venusian swung up his own long-barreled expoder!