He nodded slowly. "We can just do it. I'll check and recheck the calculations meanwhile--get the dial settings exact. And the next try--Well, it's make or break anyway." His voice was grim. "One more chance, and we get it or we don't." During that half hour he checked and counter-checked his figures until he was as sure as possible to hit the exact instant in the past--the instant when Corvo North had jotted down the lost formula. At eleven-thirty, the headset was replaced on Corvo North's head. This time his arms were left free and a pad of paper placed on his lap. His fingers held a pencil. He leaned back and again closed his eyes. Roger Kay turned the dials. Corvo North's face tensed, then relaxed. His eyes remained closed. For a half minute, aside from the faint hum from the machine, there was utter stark silence in the laboratory. It was maddening. Then a faint scratching sound. The others, holding their breath from sheer suspense, saw the pencil in Corvo North's hand begin to move across the pad. Three lines it wrote; stopped. The formula! * * * * * Suddenly the scientist's eyes snapped opened, widened with terror and bewilderment. With a movement so swift that no one could stop him, he ripped the sheet of paper from the pad, crumpled it, and hurled it at the glowing coil of an electric heater! The paper flashed into flame, crumpled into ash as Corvo North himself crumpled, went limp in the chair. Roger Kay turned the dials back to zero as Ann and the doctor leaped forward, unstrapped the unconscious scientist. Dr. Dane felt the fluttering pulse, then picked up the frail body and headed for the living quarters. Ann, her blue eyes wide with anxiety, ran ahead to open doors and prepare for the doctor's ministrations. When she returned, Roger Kay stood before the visi-screen. Ann put a hand on his shoulder. "Dad will be all right," she said, her voice flat with despair, "but we've failed. Dr. Dane says it will be days before he'd dare--" "Shh," said Roger gently. "Watch." He slipped his left arm around her slim waist, drew her to toward the screen. The vista past the purple range showed at once that the view was eastward from the spaceport. There was no shipping in sight. In the red sky, far out and very high, was a thin silvery line, growing larger. "The invaders." Unconsciously, Roger Kay whispered rather than spoke. "A thousand spheres at least for us alone. Watch, in a moment we'll know." "Know what, Roger? Do you mean--" The visi-screen answered for him. Out there high up in the sky there was a single bright flash--and then a thousand flashes that blended into one blinding one. A roar from the receiver rose to deafening pitch, stopped abruptly. [Illustration: _"Shh," said Roger gently. "Watch." He drew her to the screen._] "Shattered the diaphragm of the transmitter," said Roger quietly. "That was trionite in action, Ann, it's all over. Your father--won!"