In 1945 Germany, 25-year-old Ellen is involved in the resistance against the Nazis. She encounters Robert, a charming English spy, and they start an affair. Ellen is tasked with gathering intelligence on Hans, a German naval officer set to become Chief Officer on the submarine U 864, which is on a covert mission. Despite her intentions, Ellen develops feelings for Hans, who is engaged to someone else but is also drawn to her. Ultimately, Ellen manages to pass on crucial details about the submarine’s exact route to Japan. The English suspected that Hitler intended to send his feared wonder weapon to the struggling Japanese. As U 864 departs, the atmosphere on board is somber due to the Germans’ deteriorating war situation.