Following an anonymous tip-off, the police break into an attic apartment in a small town in the province of Brescia and discover the naked body of a schoolgirl hanging from the rafters in an apparent suicide. The autopsy reveals that the victim, 15-year-old Silvia Polvesi Sherry Buchanan, was approximately two months pregnant. While reviewing footage of a student demonstration, Assistant District Attorney Vittoria Stori Giovanna Ralli and Inspector Valentini Mario Adorf see Silvia enter a different building around the time of her death, leading them to suspect that Silvia was murdered and that the killer moved her body to the attic.
Valentini hands the case to Homicide Inspector Silvestri Claudio Cassinelli. During an inspection of the crime scene, a middle-aged man is arrested for taking photographs from a nearby building. The man, Bruno Paglia Franco Fabrizi, had been photographing Silvia with a young man in the attic. Inspector Silvestri tracks down and questions the young man in the photos, Marcello Tosti Paolo Turco, who has an alibi. The police discover the apartment where Silvia was murdered. Inside, they find a tape recorder, and the bathroom walls are smeared with blood, signaling a second victim.
The police release Paglia for lack of evidence. Silvia’s mother, Mrs. Polvesi Marina Berti, tells Vittoria that she found birth control pills in her daughter's coat pocket and had hired a private detective, Ruggero Talenti, who later dropped the case. The investigators uncover Talenti’s dismembered remains wrapped in plastic bags inside the trunk of his own car. Talenti’s secretary and mistress, Rosa Micaela Pignatelli, is in hospital recovering from a car accident, too distressed to answer questions.
That night, Rosa calls Silvestri and asks for help, saying she now wants to cooperate. A cleaver-wielding serial killer wearing black leather and a motorcycle helmet sneaks into the hospital and threatens Rosa, demanding to know where she “hid the stuff.” Silvestri and his colleague Napoli arrive just in time to save her; the killer slashes Napoli’s hand and flees on a motorcycle through a nearby train tunnel.
Back at the hospital, Rosa reveals tape recordings hidden in a vent. The recordings expose an underage prostitution ring run by powerful men. Vittoria plays one recording for Mrs. Polvesi, who confirms Silvia’s voice can be heard. The police learn of a butcher who recently bought a motorcycle, and Sergeant Giardina [Ferdinando Murolo] obtains a photograph of the suspect from his father, who says his son left home three months earlier.
One night the killer attacks Vittoria in her apartment building’s parking garage, but she narrowly survives. The hunt for the butcher named Roberto Meichiorri continues, and a photograph is shown on television. Valentini’s teenage daughter, Patrizia Roberta Paladini, reveals that she learned about the prostitution ring from Giuliana Bigi Adriana Falcão, a classmate. Giuliana tells the police that Paglia recruited her into the ring. Meanwhile, the killer murders Paglia at his home. To bait the culprits, Silvestri tells the press that Paglia survived the attack and has confessed to the police.
When the local newspaper publishes the false confession, Silvia’s psychiatrist, Professor Beltrame Steffen Zacharias, is found dead in his bathtub, apparently a suicide. One of Beltrame’s former patients, Laura Renata Moar, tells Vittoria that the professor used to drug and sexually abuse her. The police unearth incriminating files in Beltrame’s office listing the names of men involved in the prostitution ring, including prominent political figures.
Two young girls call the police claiming they spotted Roberto near a piazza. The police close in, surrounding the area. When Roberto emerges from a building on his motorcycle, attempting to shoot his way out, the officers shoot him dead. In the end, Silvestri’s superiors discourage any prosecution of the ring’s organizers, arguing that it would take months to bring evidence to court, and with the killer already dead, a conviction seems unlikely.
