A man, Jerzy, enters a train set for the Baltic coast. He seems to be on the run from something. He has to share sleeping-compartment with a woman who also seems to be on the run. Eventually we get to know that the police are looking for an escaped murderer. Is it really Jerzy they are looking for?

Marthe, a young woman, leaves her lover, Stachek, and travels to the seashore. She buys a ticket from a stranger, boards a night train, and finds herself sharing a compartment with a man. Stachek stands on the platform, pleading with Marthe to stay, as the train leaves the station. Marthe ignores him and learns that her traveling companion is a surgeon who is upset over an unsuccessful operation in which a patient died. Marthe and the doctor are drawn to each other. Suddenly, the train stops and police enter, searching for a murderer who is supposed to be in Marthe's compartment. The doctor is suspected at first, until Marthe identifies the stranger in the next compartment as the man who sold her a ticket. He is chased and captured by police, and the train resumes the trip. At the journey's end, the doctor is met by his wife, and Marthe is left alone.