Leonardo DiCaprio, Matt Damon, Jack Nicholson, Mark Wahlberg, Martin Sheen, Ray Winstone, Vera Farmiga, Anthony Anderson, Alec Baldwin, Kevin Corrigan.
In South Boston, the state police force are waging a war on Irish-American organized crime. Undercover cop Billy Costigan is assigned to infiltrate the mob syndicate, which is run by gangland chief Frank Costello. Billy quickly gains Costello's confidence. But when it becomes clear to both the mob and the police that there are moles in their midst, Billy and the other mole are suddenly thrust into danger. Afraid of being caught and exposed to the enemy, each must race to uncover the identity of the other man in time to save himself.