_What were they doing to his mind?_ He screamed out in horror, and followed the echoes of his own scream as he ran down the stone corridor, blindly, slipping on the wet stone floor, falling on his knees into inches of brackish water, scraping back to his feet with an uncontrollable convulsion of fear and loathing, only to run more-- The corridor suddenly broke into two and he stopped short. He didn't know how far, or how long, he had run, but it suddenly occurred to him that he was still alive, still safe. Only his mind was under attack, only his mind was afraid, teetering on the edge of control. And this maze of dungeon tunnels--where could such a thing exist, so perfectly outfitted to horrify him, so neatly fitting into his own pattern of childhood fears and terrors; from where could such a _very individual_ attack on his sanity have sprung? From nowhere except.... _Except from his own mind!_ For an instant, he saw a flicker of light, thought he grasped the edge of a concept previously obscure to him. He stared around him, at the mist swirling down the damp, dark corridor, and thought of the rat that had melted in his hand. Suddenly, his mind was afire, searching through his experience with the strange not-men he had learned to detect, trying to remember everything he had learned and deduced about them before they began their brutal persecution. They were men, and they looked like men, but they were different. They had other properties of mind, other capabilities that men did not have. They were not-men. They could exist, and co-exist, two people in one frame, one person known, realized by all who saw, the other one concealed except from those who learned how to look. They could use their minds; they could rationalize correctly; they could use their curious four-dimensional knowledge to bring them to answers no three-dimensional man could reach. _But they couldn't project into men's minds!_ Carefully, Harry peered down the misty tunnels. They were clever, these creatures, and powerful. Since they had discovered that he knew them, they had done their work of fear and terror on his mind skillfully. But they were limited, too; they couldn't make things happen that were not true--fantasies, illusions.... Yes, this dungeon was an illusion. It _had_ to be. He cursed and started down the right-hand corridor, his heart sinking. There was no such place and he knew it. He was walking in a dream, a fantasy that had no substance, that could do no more than frighten him, drive him insane; yet he must already have lost his mind to be accepting such an illusion.