Chicago February 14th 1929. Al Capone finally establishes himself as the city's boss of organised crime. In a north-side garage his hoods, dressed as policemen, surprise and mow down with machine-guns the key members of Bugs Moran's rival gang. The film traces the history of the incident, and the lives affected and in some cases ended by it.
Young Treasury Agent Elliot Ness arrives in Chicago and is determined to take down Al Capone, but it's not going to be easy because Capone has the police in his pocket. Ness meets Jimmy Malone, a veteran patrolman and probably the most honorable one on the force. He asks Malone to help him get Capone, but Malone warns him that if he goes after Capone, he is going to war.
Mike Sullivan works as a hit man for crime boss John Rooney. Sullivan views Rooney as a father figure, however after his son is witness to a killing, Mike Sullivan finds himself on the run in attempt to save the life of his son and at the same time looking for revenge on those who wronged him.