Markten's young assistant obeyed, and started working his way into one of the few still-standing corridors. He moved cautiously, remembering his training. When exploration of ruins of shattered masonry is indicated, guard against unnecessary vibrations.... The ruins yielded nothing but broken stone and twisted steel. There could, of course, be an obscured entrance to some lower level--many amazing documents had been discovered in the almost untouched lower levels of what had seemed totally destroyed buildings when viewed only from the gutted streets. That was why it took so long to search a city, even though there often seemed nothing left to search. There could always be some spot undetectable but intact.... When he found the opening that led downward, it was necessary to go through it and descend without contacting Markten. To shout would mean dangerous vibrations--and to go back could well mean hours of delay in rediscovering his find. The night-lamp pushed relentlessly against the blackness that hung stagnant in the lower level, and picked out the stumbling blocks of debris which had to be moved as smoothly as their weights would permit. Some were larger than the young researcher himself, and he realized that the going would have been a lot better had he not rationalized about contacting Markten to make whatever finds there might be on his own. There were many brick and girder-cluttered places that once had been rooms, but, like so many other shattered interiors he had examined, all but stone and steel had been disintegrated by the unthinkable shock-waves that must have accompanied what awful force it had been that had wreaked such havoc over the face of an entire globe. Objects made of less sturdy stuff had been literally torn molecule from molecule, atom from atom. The chance of discovery of a complete book had been computed as a near impossibility. The finding of a complete blueprint or set of diagrams was considered almost as hopeless. To find all the pieces of a plan which had merely been shattered was about the best that could be expected. And, for forty years, now, as Markten had said, it had been done by four million painstaking Research Builders. It was, in a way, amazing how so many thousands of different things had been built.... * * * * * The lamp's roving beam fingered something quickly, fell back into blackness, then was suddenly groping with the desperation of an almost uncontrolled excitement for what it touched and lost. It touched again.... Should he find Markten now? No, not yet! Perhaps what he saw would be nothing. Pinned beneath one of the most massive steel girders he had yet seen, they were-- Books! Four books! Quickly, yet with his nervous system under a willed rigidity, he assembled the portable cutting torch and began freeing his one-in-a-million find from the great length of twisted steel which held it in a vice-like hold against an embedded section of stone flooring.