In December 2016, the Bulletin of Atomic Scientists moved their iconic "Doomsday Clock" thirty seconds forward to two and a half minutes to midnight, the latest it has been set since 1952, the year of the first United States hydrogen bomb test. But a group of scientists--geologists, engineers, and physicists--has been fighting to turn back the clock. Since the dawn of the Cold War, they have advocated a halt to nuclear testing, their work culminating in the Comprehensive Test Ban Treaty, which still awaits ratification from China, Iran, North Korea--and the United States. The backbone of the...