By the summer of 1945, the United States, Britain, and China have issued the Potsdam Declaration demanding Japan's unconditional surrender. Japan's government keeps fighting, and the film follows the chain of decisions that leads President Harry Truman to authorize the atomic bomb. It reconstructs the planning room where that choice is made, then moves aboard the Enola Gay for the flight over Hiroshima on August 6, 1945, tracking the bomb known as Little Boy from the bay doors to detonation. The film renders the explosion itself in detail, then turns to its aftermath in the city: buildings leveled, fires spreading through what remains, and survivors left with injuries and radiation effects that outlast the blast by years. Archival material and reconstructed scenes carry the account of both the military reasoning behind the strike and the human cost on the ground, framing Hiroshima as the moment nuclear weapons stopped being theoretical and became a fact governments would have to live with.