He was near the top now. The last pitch was very steep and covered with huge rocks. But what was that faint flicker in his mind? It ebbed and then was back, a little stronger. A roiling, a hand dipping through his skull and stirring his brains. He clenched his fist harder and hauled himself over another boulder. The mertha were getting closer. The flashes were stabbing harder into his brain now. But how close was that? He had no way of telling. Were they behind him? Or in front? The torment in his mind had no direction. He sobbed as he climbed. He was on top of the ridge and Zadda City lay in the next valley. Maybe he would make it. But it was getting harder and harder to think, his mind was racked with even greater force. They were getting closer and closer. Hurry, run, run. But were they behind him? Oh, galaxy, had they circled and come up the ridge in front of him? They were closing in ahead of him, he felt it in every searing stroke which flashed through his brain. He turned sharp right and ran stumblingly along the ridge. Was it a trifle easier? Yes, the flashes were fainter. He ran faster and faster. The torment eased still more and a pale spectre of hope crept into his mind. And then fled. Ahead of him was the end of the ridge, a cliff, vertical and smooth. Before he could scarcely wonder if he had time to turn back, he knew he hadn't. His mind again flinched as a mental blast hit it. There was a small cabin standing alone at the very edge of the cliff. The windows were tightly boarded and it was evidently derelict. The door hung partly open and through it the fugitive scrambled. He slammed the door shut and by force of desperation managed to shoot the rusty bolt into the hasp. Inside he stood, wincing occasionally from a thrust into his mind, and staring dumbly and despairingly around the barren room. But it wasn't quite barren. A gleam of hope calmed his mental torture when he saw an old shirt and pair of work pants hanging from a hook in a far corner of the room. He dashed across the floor, tearing his prison garb off as he went. The dust from the old clothes almost choked him as he flung them on. He cast his hated prison garb into a dark corner and stamped on it. Then he rushed to the door. He had his hand on the bolt, ready to shove it open, when realization finally came to him. He sank to the floor, numbed. No physical disguise could fool the mertha or the prison guards. They tracked minds, not bodies or uniforms. The dreaded mertha gnawed a man's very brain.