Joan is recruited to work for the wartime Tube Alloys project to build an atomic bomb for Britain and meets the scientist, Max. Leo tries to recruit Joan to spy for the Soviet Union, but she rejects his appeal and ends her relationship with him, accusing him of using her. Joan falls in love with Max, but their relationship ends when Max tells her that he wants Joan as his wife, not his mistress, but Britain's divorce laws prevent him from getting a divorce because his wife will not agree to it. In 1945, Joan is appalled by the atomic bombings of the Japanese cities of Hiroshima and Nagasaki, and is frightened when it is suggested that Britain develop its own atomic bombs to possibly use against the Soviet Union. Joan contacts the Galiches to provide information about the British nuclear programme to the Soviet Union.
