An unassuming mystery writer turned sleuth uses her professional insight to help solve real-life homicide cases.

A young peasant, Aldo Contini, come to Rome in search of a job. In order to observe two women who are sunbathing on a terrace, he climbs up to a roof, not knowing that he is on the roof of a palace, in which has been killed a little girl. Forced to escape, on his own from the moment in which someone discovers the corpse, he is mistaken for the assassin and only the providential participation of a policeman succeeds in saving him from the furious vengeance of an angry mob. In possession of some clues, he is subjected to a brutal interrogation by the police, during which Aldo, after having uselessly protested his innocence of the crime, ends up confessing to the crime in front of the enquirers.