When socialite and heiress Julie Wardh begins receiving blackmail letters attributed to a mysterious serial killer, she suspects her cruel and sadistic former lover Jean is behind them. With her husband Neil frequently out of town, she falls into the arms of her friend's cousin George, and as the unknown assassin begins to make his move, she fears that one of the three men in her life may be the killer.
Just out of prison, ex-con Ugo Piazza meets his former employer, a psychopathic gangster Rocco who enjoys sick violence and torture. Both the gangsters and the police believe Ugo has hidden $300,000 that should have gone to an American drug syndicate boss. Caliber 9 is the first part in Di Leo's "Milieu" Trilogy of poliziotteschi films. It was followed by "The Italian Connection" (1972) and "The Boss" (1973).
When a shipment of heroin disappears between Italy and New York, a small-time pimp in Milan is framed for the theft. Two professional hitmen are dispatched from New York to find him, but the real thieves want to get rid of him before the New York killers get to him to eliminate any chance of them finding out he's the wrong man.
