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.