Two men, pulling trucks loaded with blueprints, accompanied Benton as he directed the work. Like caddies, they furnished the desired print when he asked for it by code number, replacing the last one in its proper place. The stocky physicist found no need to mask his thoughts while he worked; his mind was too occupied with the task at hand. Yet far back in his subconscious was a mounting tension as the day passed, hour by hour. Each minute and each soldered connection was bringing him closer to the next step in his nebulous plan. And it was this step which would determine the success or failure of his strategy. Twenty-four circuits, all inter-related in their connections to the immense bank of memory cells, had been immobilized. That was a necessary part of the project; with the new tubes, these circuits would be in much finer balance. They would operate with greater speed than before, when twice as many tubes had been used. There was one joker involved in this greater efficiency; that lay in the fact that, while the new hook-up eliminated many parts--with their frequent failures and necessary replacements--it also made the control circuits more interdependent. A single defective tube, with its many functions, could put a dozen circuits out of operation. This disadvantage had been discounted, however, for it took only a minute to replace the tube and the necessity would be rare; the more complicated system being replaced had so many parts that they were breaking down and being repaired incessantly. Dr. Albie fully expected that the crew would be able to get along with fewer technicians, men who could better be used to maintain other parts of the vast mechanism. But--and Benton kept the knowledge carefully away from his surface thoughts--one of the tubes they had already installed was defective! Urei, he was certain, had no knowledge of this fact. If he had, he would certainly have prevented its installation. Only Benton was aware of it, for he was the one who had tested the tubes when they arrived. He had designed a special circuit for the job, for none of the testing equipment on hand would take tubes with sixty-four leads. He had detected the faulty one and marked its box, placing it with the set of spares which was included in the order. He had intended to ship it back when a new order was placed, but that hadn't happened yet. There was no hurry, for with a complete replacement set he might not need new ones for a year or two. _But Benton had selected the replacement set to be used in the new installation._