Tim Koeth peered into the crumpled brown paper lunch bag; inside was a surprisingly heavy black metal cube. He recognized the mysterious object instantly—he had one just like it sitting on his desk at home. It was uranium metal, taken from the nuclear reactor that Nazi scientists had tried—and failed—to build at the end of World War II. This unexpected gift, wrapped in a piece of paper inscribed with a few cryptic but crucial lines, would launch Koeth, a nuclear physicist and professor, and his colleague Miriam Hiebert, a cultural heritage scientist, on an odyssey to trace the tale of...