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. While an undercover cop curries favor with the mob kingpin, a career criminal rises through the police ranks. But both sides soon discover there's a mole among them.
Leonardo DiCaprio
Billy
Matt Damon
Colin
Jack Nicholson
Costello
Mark Wahlberg
Dignam
Martin Sheen
Queenan
Ray Winstone
Mr. French
Vera Farmiga
Madolyn
Anthony Anderson
Brown
