Milano calibro 9 is the first part in Di Leo's Milieu Trilogy. The film was followed by La mala ordina (Manhunt) in 1972 and by Il boss (The Boss) in 1973.
Plot
Small-time gangster Ugo Piazza (Gastone Moschin) is released from prison. He tries to convince the police, the mafia, his psychotic ex-friend Rocco (Mario Adorf) and his girlfriend Nelly Bordon (Barbara Bouchet) that he wants to go straight, but everyone believes he has $300,000 of stolen money hidden somewhere.