A woman is found murdered in a closed amusement park. A young couple who happen to be there at the same time become, without their knowledge, suspects for the murder. They are chased by a large number of police but only Martin Beck believes them to be innocent.

The year 1957 was one of the most prolific for the Swedish filmmaker Ingmar Bergman: he shot two films, released two of his most celebrated films and produced four plays and a TV movie while juggling with a complicated private life.

Arthur, a university professor, and former political activist, lives in France with Francesca. They decide to hire a young man in order to help the teacher organize his notes. The employee leaves his girlfriend Ingrid and moves in with the couple.