Just after the end of World War II, a young American of German descent, Leopold Kessler, comes to the U.S.-occupied zone of Germany and gets a job with his uncle as a sleeping car conductor for the railway company Zentropa. Fresh faced and idealistic, Kessler has come to work in Germany as his "small contribution to making the world a better place," but has difficulty adapting to German customs. Kessler meets a young German woman, Katharina, the daughter of the founder of Zentropa, Max Hartmann. She points out bodies that have been hanged on trees outside the train, and explains that they are members of
Werwolf, a Nazi guerilla terrorist organization that continues to sabotage the Allied occupiers. Katharina invites Kessler to dinner at her half-bombed family mansion, where he meets her older brother, Lawrence Hartmann, and her father, Max Hartmann. Also present is U.S. Army Colonel Harris, who gives Max Hartmann a special survey: if it is found that Hartmann colluded in any capacity with the Nazi government, a near certainty given the scope of his operation, his company will be taken away from him. Harris recruits a hesitant Kessler to keep his eyes open for Werwolf activity on the trains. Kessler does not have to wait long before discovering Werwolf activity, as a man claiming to be a friend of the Hartmann family gives Kessler two children to watch during his next train outing. It is then revealed that the Werwolf group recruited one of the boys on a
suicide mission to assassinate someone on the train. The day of the survey arrives. Colonel Harris secures false testimony from a Jewish American to claim that Max Hartmann rescued him from the Nazis, in order to rehabilitate the Zentropa founder, but Hartmann later commits suicide out of shame. Leopold and Katharina have sex, and she reveals that she was formerly a Werwolf: after leaving the group, they sent blackmail letters to her father, threatening to reveal her involvement. Kessler stops the train in order to facilitate Max Hartmann's funeral, which is not permitted by the U.S. occupiers. After the funeral, Werwolf agents pull Kessler into a car, and formally ask him to join their side against the Americans, but he is hesitant. Kessler falls in love with Katharina, who asks him to marry her. On their honeymoon, she reveals that Zentropa trains carried
human transport during the war, the likely reason for her father's suicide. They settle into married life, and live happily for a time. One day, Katharina is apparently kidnapped by the Werwolf group, who also kill Lawrence Hartmann. The group demands that Kessler use explosives to blow up the train during a bridge crossing. Due to the stress of his wife's kidnapping, and deciding whether or not to bomb the train, Kessler flubs an important professional examination, infuriating his uncle. Kessler plants the explosives, and runs off the train. However, pity for the potential victims inspires him to climb aboard again, and disable the bomb. Colonel Harris and the U.S. forces uncover the Werwolf cell, and Kessler finds Katharina in handcuffs. She was a Werwolf all along, and as well as faking her own kidnapping, she herself sent the extortionate letters to her father. She expresses disgust at Kessler's cowardice in refusing to commit to a side, and says Kessler should have blown up the train, because there are no innocent people in Germany—during the war years, its citizens either killed or betrayed. Driven to despair, Kessler reluctantly decides to detonate the explosives after all. The train crashes into the river and several people are killed, including Kessler's uncle and Katharina. Kessler too is drowned in the sunken train, and floats out to sea. == Cast ==