With no hesitation, the Green stationed at the guard-post by the shaft entrance signalled Aram and his guide through. There was a short walk up a spiralling ramp and then they stood before what appeared to be simply a blank wall. Jerrold stared in perplexity as his guard took a bit of metal from his tunic and held it to the wall. "Isotope," said the guard shortly, "It acts as a key to the scanner ... below." Before Aram could question him, the section of wall slid back soundlessly and they stepped into a tubecar. Quickly, the Green set up a complicated series of stops on the tubecar controls and the vehicle started downward with a rush. Aram clutched at the man for support. Something was not as it should be. Then, quite suddenly, he realized what it was. The tubecar was travelling _down_ ... and the Fortress lay above! "Where are we going?" he asked cautiously. The Green shook his head. "Aren't the condemned cells above in the Fortress?" "Be quiet. Talk is dangerous!" "But...." "Be quiet," the Green said again. "You'll understand soon enough. We have to be careful. Not all of us here are of the Group." He turned his back on Jerrold. Aram's head was spinning. What was there on Atmion that a Green need fear? And what was this ... Group? With a wisdom born of his long imprisonment, Aram Jerrold decided to hold his peace. What would be would be, and it was becoming increasingly plain that he was about to learn of things that he had not dreamed existed. After what seemed to be an interminable period, the tubecar began to slow. The hum of atomics died and the car came to a stop. They must be well below the level of the Fortress now, reflected Jerrold, and very likely under the sea. The panels slid away and in front of them stretched a long white corridor lighted by dim bulbs set in the curved ceiling. "There are miles of tubeways down here," said the guard, "and only the isotope key gives entrance. The central pattern on the tubecar has been altered, too ... for the safety of the Group. Follow me." At the end of the corridor, a steelite door barred further progress. The Green produced his isotope key again and touched it to the metal. "A word of advice," he said to Jerrold coolly. "Listen and believe. A great many risks have been taken and a vast amount of work done to bring you this far." He leaned forward and shoved the metal door open. Within lay a brightly lit chamber. The glare of it hurt Jerrold's eyes and he stood a moment, blinking on the threshold. Slowly, as his eyes accustomed themselves to the light, Aram became aware of a group of men and women who watched him impassively. There were a few in Fleet uniform. One or two of them casual acquaintances he had thought lost in space or imprisoned by the Greens. There were others in prison garb, and here and there he could see the dread color of the Security Police. His heart began to pound. Another trap? But why?