Based on a true incident, this tells the story of a troubled young man who kills his sister's reactionary, violent and abusive husband and is eventually arrested for the murder. However, the dead husband happened to be a member of the Italian nobility, and the trial starts to turn into more of a prosecution of the defendant's socialist politics and the activities of his father, a well known liberal social reformer, than the actual crime itself.

A university student, Mario Buongiovanni, tries to do various jobs to pay for his studies: selling encyclopedias, singing in night clubs, being a tour guide. He then became a science teacher in a female college, where he met Lisa, the daughter of a Lombard industrialist, whom he fell in love with. But Lisa's father, unfortunately, already has in mind for her a marriage with a very rich suitor ...