In November 1944, 18-year-old June Walker boards an unmarked bus, destined for Oak Ridge, Tennessee, which has sprung up in a matter of months. There, June joins hundreds of other young girls operating massive machines whose purpose is never explained. They spend their evenings socializing and flirting with soldiers, scientists and workmen. June longs to know more about their top-secret assignment and begins an affair with Sam Cantor, a young Jewish physicist who oversees the lab where she works and understands the end goal only too well. Across town, African-American construction worker Joe Brewer knows nothing of the government’s plans. But a breach in security will intertwine his fate with June’s search for answers.