Colin Sullivan (Damon) is introduced to organized crime by Irish mobster Frank Costello (Nicholson) in the Irish neighborhood of South Boston. Costello trains him to become a mole inside the Massachusetts State Police. Sullivan is accepted into the Special Investigations Unit, which focuses on organized crime. Before he graduates from the police academy, Billy Costigan (DiCaprio) is asked by Captain Queenan (Sheen) and Staff Sergeant Dignam (Wahlberg) to go undercover, as his family ties to organized crime make him a perfect infiltrator. He drops out of the academy and does time in prison on a fake assault charge to increase his credibility.
As both infiltrate their respective organizations, Sullivan begins a romance with psychiatrist Madolyn Madden (Farmiga). Costigan sees her for his probation and also develops a relationship with her. After Costello escapes a sting operation, both moles become aware of the other's existence. Sullivan is told to find the "rat" and asks Costello for information to determine who is the informer within his crew. Costigan follows Costello into a movie theater where Costello gives Sullivan an envelope. Costigan then chases Sullivan through Chinatown. When it is over, neither man knows the other's identity. Sullivan has Queenan tailed to a meeting with Costigan. Costello's men go in and Queenan is killed. When they exit, Costigan pretends he has come to join them. Later, Costello's henchman, Fitzgibbons (O'Hara), reveals that Delahunt, a crew member, was an undercover cop.
Brad Pitt|Brad Grey|Graham King
October 6, 2006