MacVickers turned, scowling. It was hot. The room above was cool by comparison. The air was thick and sluggish with the reek of heated oil and metal. It was a big space, running clear to the curving wall, but the effect was of stifling, cramped confinement. Machinery crammed the place, roaring and hissing and clattering, running in a circuit from huge intake pumps through meaningless bulking shapes to a forced-air outlet, with oil-pumps between them. The pumps brought mud into a broad sluice, and the blue-green stain of it was everywhere. There were two glassite control boxes high on the walls, each with a black, tentacled Europan. About five feet overhead was a system of metal catwalks giving complete coverage of the floor area. There were Europans on the walks, too, eight of them, patrolling steadily. Their sleek, featureless bodies were safe from contact with the mud. They carried heavy plastic tubes in their tentacles, and there were heavy-duty shockers mounted at every intersection. MacVickers grinned dourly. "Trustful lot." "Very." Pendleton nudged him over toward a drive motor attached to some kind of a centrifugal separator. Loris and the blue-sheathed Earthman followed, with Birek coming slowly behind him. MacVickers said, "What's all this for?" Pendleton shook his head. "We don't know. But we have an idea that Jovium comes from the mud." "Jovium!" MacVickers' grey-green eyes began to grow hot. "The stuff that's winning this war for them. The metal destroyer!" "We're not sure, of course." Pendleton's infinitely weary eyes turned across the stretch of greasy metal deck to the end of the circuit. "But look there. What does that suggest to you?" The huge pipe of the forced-air ejector ran along the deck there behind a screen of heavy metal mesh. Just above it, enclosed behind three thicknesses of glassite, was a duct leading upward. The duct, from the inordinate size of its supports and its color, was pure lead. Lead. Lead pipe, lead armor. Radiations that changed living men into half-living diamonds. Nobody knew what Jovium was or where it came from--only it did. But scientists on the three besieged worlds thought it was probably an isotope of some powerful radioactive metal, perhaps uranium, capable of setting up a violent progressive breakdown in metallic atoms. "If," said MacVickers softly, "the pipe were lined with plastic.... Blue mud! I've traded through these moons, and the only other deposit of that mud is a saucepanful on J-XI! This must be their only source." Loris shoved an oil can at him. "What difference does it make?" he said savagely. MacVickers took the can without seeing it. "They store it up there, then, in the space between the inner wall and the outer. If somebody could get up there and set the stuff off...." Pendleton's mouth twisted. "Can you see any way?" He looked. Guards and shockers, charged ladders and metal screens. No weapons, no place to conceal them anyway. He said doggedly: