On August 29, 1949, the first Soviet test bomb, dubbed "First Lightning," exploded in the deserts of Kazakhstan. This surprising international event marked the beginning of an arms race that would ultimately lead to nuclear proliferation beyond the two superpowers of the Soviet Union and the United States. With the use of newly opened archives, Michael D. Gordin follows a trail of espionage, secrecy, deception, political brinksmanship, and technical innovation to provide a fresh understanding of the nuclear arms race.