Young Treasury Agent Elliot Ness arrives in Chicago and is determined to take down Al Capone, but it is not going to be easy because Capone has the police in his pocket. Ness meets Jimmy Malone, a veteran patrolman and probably the most honourable one in 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.