Like almost everything else, the power-cartridge plant was airtight and had its own oxygen-generator. The air-analyzer reported the oxygen insufficient to support life. That was understandable; there were a lot of furnaces which had evidently been hot when the power was cut off; they had burned up the oxygen before cooling. They put on their oxygen equipment when they got out of the car. "I'll go back and have a look at the power plant," Matsui said. "If it's like the rest of this place, it'll be ready to go as soon as the reactors are started. I wish everybody here had left things like this." "Well, we'll have to check everything to make sure nothing was left on when the main power was cut," Conn said. "Don't do anything back there till we give you the go-ahead." Matsui nodded and set off on foot along the broad aisle in the middle. Conn looked around in the dim light that filtered through the dusty glass overhead. On either side of the central aisle were two production lines; between each pair, at intervals, stood massive machines which evidently fabricated parts for the power cartridges. Over them, and over the machines directly involved in production, were receptor aerials, all oriented toward a stubby tower, twenty feet thick and fifty in height, topped by a hemispherical dome. "That'll be the control tower for all the machinery in here," he decided. "Anse, suppose you and I go take a look at it." "We'll take a look at the machines," Rivas said. "Clyde, you and I can work back on the right and then come down on the other side. You know anything about this stuff?" "Me? Nifflheim, no," Nichols said. "I know a robo-control when I see one, and I know whether it's set to receive or not." There was a self-powered lift inside the control tower. Conn and Anse rode it to the top and got out, Anse snapping on his flashlight. It was dark in the dome at the top; instead of windows there were viewscreens all around it. Five men had worked here; at least, there were four chairs at four intricate control panels, one for each of the four production lines, and a fifth chair in front of a number of communication screens. There was a heavy-duty power unit, turned off. Conn threw the switch. Lights came on inside, and the outside viewscreens lit. They were examining the control-panels when Conn's belt radio buzzed. He plugged it in on his helmet. It was Mohammed Matsui. "There's one big power plant back here," the engineer said. "Right in the middle. It only powers what's in front of it. There must be another one in either wing, for the isotope plant and the cartridge-case plant. I'll go look at them. But the power's been cut off from the machines in the main building. There's four big switches, one for each production line--" He was interrupted by a shout, almost a shriek, from somewhere. It sounded like Jerry Rivas. A moment later, Rivas was clamoring: "Conn! What did you turn on? Turn it off, right away!"