Uploaded April 2013 | Updated September 2026, 1 week ago
Colin Sullivan (Damon) is introduced to organized crime by Irish-American 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 men infiltrate their respective organizations, Sullivan begins a romance with psychiatrist Madolyn Madden (Farmiga). Costigan sees her for his probation and develops a relationship with her, as well.
After Costello escapes a sting operation, both moles become aware of each other's existence. Sullivan is told to find the "rat" and asks Costello for information to determine who is the informer within his crew.
Colin Sullivan (Damon) is introduced to organized crime by Irish-American 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 men infiltrate their respective organizations, Sullivan begins a romance with psychiatrist Madolyn Madden (Farmiga). Costigan sees her for his probation and develops a relationship with her, as well.
After Costello escapes a sting operation, both moles become aware of each other's existence. Sullivan is told to find the "rat" and asks Costello for information to determine who is the informer within his crew.
