The Marziales are an important family from Viterbo and in the garden of their villa a retired friend of Rocca's body is found, whose wife had died suspiciously, hit by a pirated car. Thanks also to the help of Francesca (who tutors a niece of the landlady), Rocca investigates the rich family, omertosa and hostile, reaching the solution of yellow.

A transvestite is the only witness to the murder of a man, found dead in a car outside a bowling alley. Even the waitress of the restaurant is later killed and suspicions seem to fall on her husband, but Marshal Rocca does not believe this is the case. In fact, the guardian of the restaurant is the real culprit, a murderer to avenge the death of his son.

A girl is found stabbed dead; she was staying in a Roman hotel. Rocca investigates her past and discovers that she had been kidnapped when she was ten years old: her parents, left broke following her payment, kill themselves. It is the kidnapper (owner of the hotel), whom the girl had recognized from a tattoo and who was following in her footsteps, who killed her. Francesca will figure out who it is from her tattoo and be saved by Rocca when the innkeeper tries to kill her.

A young pediatrician dies after drinking coffee in which a substance to which he was allergic was dissolved. Whoever killed him is not the father of a little dead patient, as it seems at first, but his nurse, in love with the doctor and unrequited. The woman had turned to a magician, later found lifeless in her home, to give her lover a love potion. Meanwhile, Francesca meets a man and informs Rocca that she intends to marry him.

Rocca is grappling with a series of crimes, which lead Mannino to think they are the work of a serial killer, who shoots a rifle belonging to a stolen batch of weapons. One of the victims is the perpetrator of the theft, Luca; the boy, together with a friend who worked at the gun shop, had planned to sell the rifles clandestinely. It is Rocca who discovers that the person responsible for the crimes is Luca's adoptive father, suffering from an incurable disease that made him lose his mind and led him to believe that his stepson had committed matricide. During the capture, the madman shoots the marshal who is saved thanks to his bulletproof vest.