When nineteen-year-old Doris Friedman marries Rob in 1941 and has a sickly, premature baby, she trades in her dreams of being a concert pianist or a lawyer to become the ideal wife and mother. Within months, Rob is recruited to work on the Manhattan Project, and the young family moves to Oak Ridge, Tennessee. Just like fission splits an atom's nucleus, Doris's marriage threatens to break her heart in two as she is left struggling to nurture her daughter while Rob works around the clock. In an effort to find connection, Doris befriends Betty, a Southern debutante. Even though they come from different backgrounds, the two women sustain each other through difficult moments: Betty's miscarriage, Rob's radiation exposure, and his subsequent attempt to enlist to fight at the front. Despite her attempts to make life in Oak Ridge work, Doris falls for an army engineer - only to realize that he may be a Soviet spy. Should she turn him in and risk losing her marriage? As the end of the war nears, Doris must decide what's most important - and what she's willing to lose.