"You're wrong," Devries replied. "Empty your pockets, quick!" Janus stared at him, uncomprehending. "That slot in the doorway!" Devries explained. "I watched how V'Naric worked that key. I can't hope to duplicate it, but if we have a pocket knife or something--we _might_ make a short circuit! Should have thought of that before." Already he was searching his own pockets, and Janus quickly followed his example. But their hopes waned. Neither of them had a knife, and what was worse, they had nothing else that might serve the purpose. Devries turned away in despair. "Wouldn't you know it! And I always carry a knife--all except this time!" Janus was still searching. Suddenly he gave a shout as he produced something from an inside pocket. A round, flat metal object. Devries saw that it was an ancient half-dollar. He had seen very few of them, and only in museums. "My good luck charm," Janus said wistfully. "I've carried it with me ever since my first space flight." Devries seized it eagerly. "We'll see how lucky it is!" He examined the narrow slot in the doorway, but its length was considerably less than the diameter of the coin. Nor could he tell how deep that slot was. "We've got to get this down to proportion," Devries said grimly. "Even then it may not work, but we've got to try anything." He began rubbing the edge of the coin against the bare stone, and the rounded edge flattened infinitesimally. "Quite a job on our hands; we've got to get this diameter down to less than half!" Taking turns, they kept at it, holding the coin in strips of cloth to protect their fingers from the heat of the metal. While one worked the other watched the doorway. Occasionally a Proktol passed by, but V'Naric did not come again. Once Janus moved to the window and ventured to look down at the Brain again, but carefully kept his gaze averted from the spot where Ketrik was. Now he could distinctly see the huge mass of the Brain pulsing with the impact of the thought-force that swelled out to it. And now it was not pale-pink, it was red. It was even more than blood-red, it seemed fiery. He could sense the pulsing power of it, the super-mental force, and it seemed diabolic. Here, he knew, was a dangerous thing, a thing that should not exist in this solar system. "Do you know what I think?" Janus said, turning back to Devries who was again working on the coin. "That Brain is mad! It's bound to be. God knows how long it's been receiving those Proktols' thought-force, living and thriving and planning on it--and that thought-force is hate! V'Naric said it's getting ambitions. Ambitions for _conquest_, I think. That's all that fleet of space-ships out there can mean!" They worked slowly but steadily with the coin, gradually wearing its diameter down to fit the slot in the doorway. What they feared mostly now was that the Proktols would very soon be through with Ketrik down there, and one of them would be next.