"The assistant inspector did accept the bribe. The welds passed the computer certification all right—because it was the same damn good weld, replicated over and over and inserted into the data bank in place of real inspections, which for the most part were never even made. Twenty propulsion chambers were put online. Twenty time bombs.

"It wasn't until the second one blew up eighteen months later that the whole story was finally uncovered. This isn't hearsay; I was on the probable-cause investigating team. It was I who found it, by the oldest test in the world, eye-and-brain inspection. When I sat there in that station chair, running those hundreds of holovid records through one by one, and first recognized the piece when I saw it again—and again—and again—for the computer only recognized that the series was free of defects—and I realized what those bastards had done . . ." His hands were shaking, as they always did at this point of the lecture, as the old memories flickered back. Leo clenched them by his sides.

"The judgment of the map was falsified in these electronic dream images. But the universal laws of physics yielded a judgment of blood that was absolutely real. Eighty-six people died altogether. That"—Leo pointed again—"was not merely fraud, it was coldest, cruelest murder."

He gathered his breath. "This is the most important thing I will ever say to you. The human mind is the ultimate testing device. You can take all the notes you want on the technical data, anything you forget you can look up again, but this must be engraved on your hearts in letters of fire.

"There is nothing, nothing, nothing more important to me in the men and women I train than their absolute personal integrity. Whether you function as welders or inspectors, the laws of physics are implacable lie detectors. You may fool men. You will never fool the metal. That's all."

He let his breath out, and regained his good humor, looking around. The quaddie students were taking it with proper seriousness, good, no class cut-ups making sick jokes in the back row. In fact, they were looking rather shocked, staring at him with terrified awe.

"So"—he clapped his hands together and rubbed them cheerfully, to break the spell— "now let's go over to the shop and take a beam welder apart, and see if we can find everything that can possibly go wrong with it. . . ."

They filed out obediently ahead of him, chattering among themselves again. Yei was waiting by the door aperture as Leo followed his class. She gave him a brief smile.

"An impressive presentation, Mr. Graf. You become quite articulate when you talk about your work. Yesterday I thought you must be the strong silent type."

Leo flushed faintly and shrugged. "It's not so hard, when you have something interesting to talk about."

"I would not have guessed welding engineering to be so entertaining a subject. You are a gifted enthusiast."