"It turns to heat!" Masters' face brightened. "And if you pen up heat, it turns to light. I learned that in school. Resistance causes a change. But what do the spheres turn to?" "Radio energy, Masters! Something absolutely harmless to man. These living, energy spheres will change to radio energy when they meet resistance. Frustration is resistance. Frustration is an emotion. An overwhelming emotion for the spheres! The sphere is frustrated--meets resistance--it disappears. In other words, it dies!" * * * * * From the city came screams and cries. The spheres had attacked at last. The men in the wooded field could see the darting balls sending their searing bolts down on the heads of hapless victims. The crashing roar of the slaughter sounded like distant thunderstorms. Streets were jammed with panic-stricken human beings, fleeing from the unknown menace which slashed with bolts of heat energy. From the hole in the factory roof poured more spheres to join the destruction. "They breed fast, the devils!" said Masters. A figure in khaki approached Taylor. It was Pember with blood running from a cut on the side of his head. He saluted briskly. "Norden escaped, sir!" he blurted. "The dirty so-and-so cracked me over the head with the trench tool and got away!" "I never thought he'd turn yellow," Masters said. "Well, maybe it's a good thing he's gone. I never trusted him anyhow." "Which way did he go?" Taylor asked. "He went toward the factory, sir!" Pember replied. "He didn't knock me out. Just a glancing blow. I was too dazed to stop him, but I saw him running toward the factory." "He'd rather take it that way than the firing squad, I guess," Masters decided. "Masters," Taylor said. "We overlooked something. Norden knows something we don't know. He was around Orkins most of the time after we left the plant. He listened to what Orkins said. Orkins was in the factory when the spheres first appeared. I overlooked Orkins as having an answer to the problem. I thought I knew it all, but I was wrong! Orkins knew more than I know about the spheres." "Sure! I should have thought of it, too. How did Orkins get away when everyone else got killed? I never asked that. I just took it for granted that he got away by accident. Orkins might have known enough to help Norden get the spheres on his side!" Taylor already was running toward the factory. At his heels came Masters and Pember. CHAPTER VI INFERNO They found no sign of Norden as they approached the factory. Several times they had to take cover in ditches and weeds as whispering spheres floated overhead in search of prey. But they escaped the electrical feelers which stirred the grass and brush around them. Pember recovered his Garand rifle, which had been left near the sentry box during the retreat. Taylor led the group into the tunnel, with Masters following and Pember bringing up the rear.