The whirring within the sphere grew louder. The floor seemed to quiver underfoot as giant motors generated energy. "Fire!" The entire sphere shuddered. Earthquaking explosions sounded outside as charges of force left the tubes to expel their power on the grey mass in the clearing. Charge after charge was poured into the attacking rat men. Ro leaped back to the porthole. He saw giant craters opening in the ground. Hoarse screams of pain and terror reached his ears. Scores of Oan were literally torn apart. Others disappeared completely. Those of the attackers who lived retreated in disorder. Ro noticed that one of the retreating Oan carried a ray gun. "Cease fire," shouted the professor. Carlson and Grimm turned from their guns laughing. "They won't be back," chuckled Grimm. "They'll keep running for a week." Ro moved silently to the post Carlson had occupied. He picked up the ray gun the Earthman had laid aside. "What do you want with that?" asked the professor. "The battle is over. There won't be any use for ray guns now. We've beaten them." "How does it work?" Ro asked grimly. His face was hard with determination. The professor was puzzled, but explained the workings of the gun. He finished his explanation with, "But why?" Ro walked to the door. "The Oan still have a gun," he said. "When you are gone, they will return to use it on my people. That must not happen." He said no more, but left the room. Na and the others heard the door of the sphere open and slam shut. Carlson was the first to recover his wits. "Come on," he said. "He may need help." The three Earthmen armed themselves and left the ship. They saw Ro disappear into the wood and took after him. Ro moved swiftly and silently. He slipped through the underbrush like an elusive phantom. Some distance from the sphere he saw a grey shadow running ahead of him. He drew a bead on the creature and fired. A feeling of power surged through him as the rat man screamed and died. He ran on. Minutes passed before he saw the second Oan. The furry beast died a flaming death without uttering a sound. Ahead of him, Ro saw a clearing. Instinctively he swerved from his course to circle it. He had gone halfway around, when his eyes caught sight of a twisted, grey body perched on a limb overlooking the clearing. It was the rat man he sought--the one with the ray gun, crouching there, waiting for Ro to step unsuspectingly into the clearing. * * * * * Ro chuckled as he caught the Oan in his sights. He pulled the trigger. Fire seared from the muzzle of the gun. The rat man screamed wildly. He crashed down from the tree, leaving a trail of broken limbs in his wake. His body struck the ground with a dull thud, thrashed hopelessly for a few seconds, then lay still. Ro laughed aloud and stepped into the clearing. He was still laughing when the three Earthmen came upon the scene.