In 1986 South Boston, Colin Sullivan is introduced to Irish Mob boss Frank Costello. Twenty years later, Costello has groomed Sullivan as a mole inside the Massachusetts State Police. Sullivan is accepted into its Special Investigations Unit, led by Captain Ellerby. Another recruit, Billy Costigan Jr., is approached by Captain Queenan and Staff Sergeant Dignam and given the choice of being kicked out based on family ties to crime or going undercover and infiltrate Costello’s crew. They set up a cover for him as an academy dropout, and he serves time in jail on a phony battery charge and joins Costello’s crew. Ellerby informs Special Investigations that only Queenan and Dignam will know their operatives’ names and that Costello’s crew has stolen computer microprocessors to sell to a Chinese gang. Costigan’s emotional state declines. Queenan and Dignam tell him there is a informant in the Special Investigations Unit and plead with him to stay until the deal takes place. The Departed 2006 full
Sullivan begins a romance with police psychiatrist Madolyn Madden. Costigan sees her professionally as part of his probation. The MSP is ready to catch Costello selling the microprocessors, but the deal takes place off-camera, and everyone escapes, enraging Ellerby. Costello realizes there is a rat. Sullivan is promoted and tasked by Costello to find the rat. Sullivan tells him to deliver information to cross-reference his crew members in the MSP database. Costigan learns that Costello is an FBI informant. Costello accuses Costigan of being a rat, but Costigan denies it. He tells Queenan that Costello is an FBI informant and is aware of a mole in his crew.
Costigan follows Costello into a theater, witnessing him giving Sullivan an envelope. Queenan gives Costigan instructions to get a visual ID of Sullivan before making the arrest. Costigan chases him but is unable to see his face. Sullivan realizes he’s being followed and prepares to stab Costigan, but kills another person by accident and escapes. He realizes he and Costigan have been captured on a security camera and tries cross-referencing officers but cannot recognize Costigan.