Young Treasury Agent Elliot Ness arrives in Chicago and is deternimed to take down Al Capone (Robert De Niro) but he learns that it's not going to be easy, because Capone (Robert De Niro) has the police in his pocket. But Ness meets Jimmy Malone a veteran patrolman and probably the most honorable one in the force. He asks Malone to help him get Capone (Robert De Niro) but Malone warns him that if he goes after Capone (Robert De Niro), he is going to war. They recruit academy cadet, George Stone and Treasury agent Oscar Wallace, who is also an accountant, who wants to prosecute Capone (Robert De Niro) for tax evasion. When they make headway, Capone (Robert De Niro) tries to get them but they are untouchable.