Just after the end of World War II, a young American of German descent, Leopold Kessler, arrives in the U.S.-occupied zone of Germany and takes a job as a sleeping car conductor for the railway company Zentropa, working with his uncle. He arrives with idealistic ambitions, hoping that his small act can help make the world a better place, but he quickly discovers that adapting to postwar life and new German customs is harder than he expected. Early encounters pull him into a tense world where loyalty, guilt, and survival collide.
In a tense social circle around Zentropa, he meets Katharina, the daughter of the company’s founder, Max Hartmann. She introduces him to the grim reality outside the train windows: bodies hanging from trees, the lingering menace of Werwolf, a Nazi guerrilla group still active in the countryside and capable of sabotage. Katharina welcomes Leopold to her half-destroyed family mansion for dinner, where he meets her older brother, Lawrence Hartmann, and her father, and where a U.S. Army colonel named Harris outlines a political minefield: if Hartmann’s dealings with the old Reich are ever proven, Zentropa could be confiscated. Harris enlists Leopold to keep a lookout for Werwolf activity on the trains, and Leopold, though uneasy, accepts the assignment, torn between his sympathy for the Occupation and a growing fear of what he’s asked to become.
Leopold’s suspicions about Werwolf deepen quickly. A man who claims to be a Hartmann ally entrusts him with watching two children on his next run, and it becomes chillingly clear that Werwolf has recruited one of the boys for a suicide mission. The day of the survey arrives, and Harris manipulates testimony—claiming Hartmann rescued a Jewish American—to polish Hartmann’s image, while the truth about Hartmann’s past deeds remains buried. Hartmann himself withdraws from life, and, overwhelmed by shame, takes his own life. Leopold and Katharina grow closer in the shadow of these secrets, and Katharina reveals a painful truth: she once belonged to Werwolf but left the group; the organization then began threatening her father with blackmail.
When Leopold halts a train for Hartmann’s funeral—a gesture the U.S. authorities would rather suppress—he finds himself entangled in a new test of loyalty. After the service, Werwolf agents lure him aside and press him to join their side. He remains oath-bound to protect the living, even as danger looms closer. The romance between Leopold and Katharina deepens, and they marry, seeking a fragile happiness as they settle into married life, unaware of how dark Katharina’s past still shadows them. On their honeymoon, Katharina confesses that Zentropa’s trains carried people to peril during the war, a revelation that helps explain her father’s despair.
Soon afterward Katharina is taken—and Lawrence Hartmann is killed—by Werwolf, who demand that Leopold use explosives to blow up a train during a bridge crossing. The stress and fear push Leopold toward failure on an important professional exam, which worsens his uncle’s anger. He plants the charges and flees, but a sudden surge of pity for potential victims compels him to climb back aboard and try to disable the bomb. The investigation by Harris and the U.S. forces closes in, and Leopold finally finds Katharina—handcuffed and revealed to have been Werwolf all along, the architect of the earlier kidnappings and the extortion letters.
Her harsh reproach cuts to the bone: Leopold’s failure to choose a side is interpreted as cowardice, and she insists that there are no innocents left in Germany’s ruined landscape. Paralyzed by doubt and despair, Leopold makes a fateful decision: he detonates the explosives in a desperate bid to stop the carnage he helped to unleash. The train plunges into the river, and lives are lost in the wreck—the uncle who believed in him, Katharina herself, and several others, even as Leopold sinks beneath the surface and finally drowns, leaving him to drift away into the open sea.
