Twelve-year-old Sachi's life is forever changed when the U.S. drops the first atomic bomb on Hiroshima, Japan, in 1945. Sachi's city is destroyed and she later moves to the U.S. to be treated for her devastating injuries. As a backdrop to Sachi's story, Yep chronicles the development of nuclear weapons, the actual attack and aftermath, the politics of the nuclear arms race, and the anti-nuclear movement.