The South Boston state police force is waging war on organized crime. Undercover cop Billy Costigan is assigned to infiltrate the mob syndicate run by gangland chief Frank Costello. While Billy quickly gains Costello’s confidence, Colin Sullivan, a hardened young criminal who has infiltrated the state police as an informer for the syndicate, is rising to a position of power in the Police Force. Each man is deeply consumed by their double lives, gathering information about plans and counter-plans of operations they have infiltrated. But when it becomes clear to both the mob and the police that there is a mole in their midst, Billy and Colin are suddenly in danger of being caught and exposed to the enemy. Starring Leonardo DiCaprio & Matt Damon.