Capone details the life of crime boss Al Capone (Ben Gazzara). Capone begins his rise through the ranks of the underworld at the age of 11. Eventually becoming a member of the Five Points Gang, run by his friend Johnny Torrio (Harry Guardino), Capone sets his sights on bigger things. Relocating to Chicago, Capone makes his move and calls for the death of his friend's uncle. Taking over, Capone then becomes one of the most powerful gangsters in Chicago. In charge of the city's prostitution and racketeering rings, Capone allows his power to go to his head, bedding some of his hookers and contracting syphilis along the way. Even with the help of fellow gangster Frank Nitti (Sylvester Stallone), Capone's physical and mental condition deteriorates as a result of the syphilis, and his empire begins to slip through his fingers. Legendary producer Roger Corman uses footage from his own earlier film about the St. Valentine's Day Massacre to flesh out the same event in this film.