A young schoolgirl becomes embroiled in the murder investigation of a prostitute, who happened to spend the night with one of the girl's male neighbors.

Sylvana, a 13-year-old schoolgirl, becomes infatuated with her handsome neighbor, Gino. A prostitute is found murdered in the building where Gino lives, and the police question everyone in the neighborhood. Because Sylvana saw Gino leaving the apartment of the murdered prostitute, Gino encourages her flirtation to prevent her from destroying his alibi. Sylvana initially withholds her knowledge, but when she later learns that Gino has lied to her, she becomes disenchanted and divulges her story to the police. Taking note of Sylvana's precocity, the police disbelieve her story, attributing her accusation to vengefulness. Inspector Fioresi advises Sylvana's mother to send her to a convent-reformatory for her own protection. Ashamed and humiliated, Sylvana makes an unsuccessful suicide attempt; Fioresi is spurred to investigate Gino's past, and he uncovers the truth. As the killer prepares to marry Lorella, an heiress, he is arrested by the inspector. Sylvana is exonerated and returns to lead a normal life with her family and friends.