A French student, Françoise Pigaut, was found stabbed in a park in Bergamo after accepting a lift from a stranger. Commissioner Berardi, in charge of the investigation, soon gathered overwhelming evidence against a television journalist called Alessandro Marchi. The latter was then sentenced to life imprisonment. Marchi's lawyer, an ambiguous man named Giulio Cordaro, zealously defended his client, pretending to be his friend, but in reality he was convinced of his guilt. He was even happy to have lost the case, since he was the lover of Maria, Alessandro's wife.
After the conclusion of the trial, Alexander's daughter Sarah, who despised her mother for her bourgeois hypocrisy and adultery, accidentally met Giorgio, a former schoolmate of hers. Giorgio was now a bohemian pianist and a protester. With his testimony in court, he had tried to exonerate Alessandro.
A relationship developed between Sarah and Giorgio, although the young man seemed strangely restless and upset. In the following days, two new murders occurred in the same park in Bergamo, with very similar methods to the murder of Françoise. This led the Court of Cassation to believe that Alessandro Marchi had been the victim of a judicial error. Consequently, it ordered the reopening of the trial. Alessandro was acquitted, also thanks to the testimony of his lover, Marta Clerici, who was abroad with a friend at the time of the first trial.
Once back at liberty, Alessandro received a phone call from Giorgio, who asked him to meet secretly in an abandoned industrial warehouse. Alessandro accepted the invitation and went to meet the young man. Here, Giorgio forced him to confess to Françoise's murder and revealed that he had committed the two subsequent murders to get him acquitted and avenge the death of the girl, who had been his fiancée. However, when Giorgio tried to kill Alessandro by shooting him, the journalist defended himself with a knife. In the ensuing scuffle, both were mortally wounded.