Lies. Betrayal. Sacrifice. How far will you take it?

To take down South Boston's Irish Mafia, the police send in one of their own to infiltrate the underworld, not realizing the syndicate has done likewise in director Martin Scorsese's crime thriller. While undercover cop Billy Costigan (Leonardo DiCaprio) curries favor with mob kingpin Frank Costello (Jack Nicholson), career criminal Colin Sullivan (Matt Damon) rises through the police ranks. But both sides soon discover there's a mole among them.