Frank Costello goes into a diner and asks if Vin’s daughter, Carmen’s, got her period yet. Costello recognises young Colin Sullivan. He gives Colin a bagful of groceries for him and his grandmother. Costello suggests Colin see him to make some extra money.
Colin’s at police academy. He plays rugby. Billy Costigan Jr is jogging with his friend, Brown. As a black guy in Boston, Brown’s completely screwed.
Colin’s welcomed to the Special Investigation Unit by Captain Queenan and the belligerent Staff Sergeant Dignam.
Ellerby tells Colin their unit is an elite one, designed to disrupt organised crime in the city in association with the FBI. Costello uses three key guys: Fitzy, Delahunt and French.
Dignam suggests Billy spoke differently when he was with the deprived part of his family and differently again when he was with the well-off part. Billy barely keeps his temper as the insults come raining down.
At his mother’s funeral, Billy finds a card signed Frank Costello. Billy’s now more determined than ever to bring down Costello. He expresses interest to Queenan and Dignam.
As a backstory, Billy will plead guilty to assault and battery. He’ll do just enough jail time to convince anyone concerned. He’ll be on probation and see a court-ordered psychiatrist.
Once released from jail, Billy tells his Aunt Cathy his mother’s dead. Billy then tells cousin Sean he’s inherited $30,000 and wants to invest it with Sean.
French knew Billy’s father, but liked Billy’s Uncle Jackie better. Billy smashes a glass over someone’s head. French tells Billy he shouldn’t have done that. French knows Billy and his family. French leaves the man on the floor for a second time.
Somebody stole twenty microprocessors from the MASS Processor company on Route 128. They help guide cruise missiles and are worth $100,000 apiece. Costello’s moving the microprocessors to China.
Colin says “hello Dad” into his phone. He tells Costello he’s being followed by a blue sedan and then a white van with graffiti. French then shakes the tails.
A store owner’s being harassed by Italians. Billy goes to pay, then beats both men down to the ground, breaking his hand.
Billy, plaster cast on his hand, is at the bar. Costello’s fed up with the local Mafia. The guys Billy beat up are gonna come back and kill him. Only Costello can call them off. French searches Billy. Costello wants the plaster cast also searched. French breaks it open, then confirms Billy’s clean.
Costello repeatedly hits Billy’s broken hand asking if Billy’s still a cop. Billy screams he’s not. Costello tells Billy to stop doing coke deals with his cousin. Costello will handle the Italians. Billy falls to the floor.
The Italians Billy beat up are dead, but Jimmy Pappas is framed for the hit. Thanks to Costello, the registered murder weapon is found in Pappas’ car.
Costello’s girlfriend Gwen says she has choir practice. Costello gets a severed hand from a bag, removing a ring from a finger. Billy’s wired for sound. Costello wants the ring sent to the victim’s wife. Billy desperately removes his wire and is told to listen out for any talk of microprocessors.
French is roughing up a man with no licence. He’s bringing undesirables into Costello’s area. A man watching reaches into his jacket. Billy cracks him in the face with his gun. The man is Jimmy Bags. French says he didn’t need his teeth anyway.
Queenan’s cleverly compartmentalising everything in the Special Investigations Unit. There may be a rat in the State police. Colin’s team don’t have access to Queenan’s undercovers.
Fitzy’s in custody for having a suspended licence. Brown has beeped Fitzy’s lawyer twice. Colin borrows a phone and turns off the camera, pretending to be Fitzy’s lawyer.
Colin asks if Fitzy’s made any statements or calls. He beeped the lawyer. Colin says Fitzy should call “his mother”. Colin says they’re already suiting up for a raid. They know where they’re going and so does Fitzy. Soon, Fitzy dials the number.
Billy’s meanwhile surrounded by drugs. French answers the phone. Fitzy says his line. French orders everybody out and lights the curtains.
Colin tells Brown the last number called is Fitzy’s house. Colin says he’ll swear to the judge he surveilled him and they’ll have a warrant.
Billy tells Madolyn he can be somewhere with a mass murderer. His heart rate is jacked, but his hand is steady. Also, he’s learned to recognise a cop: by their bad haircut, lack of dress sense and air of scumbag entitlement.
Billy tells Dignam and Queenan he’s had enough. Dignam reminds Billy they’re the only two people in the world who know Billy’s still a cop. Dignam threatens to erase Billy’s file. Billy attacks Dignam. Queenan thinks Costello has a spy inside the SIU.
Billy comes to see Madolyn for valium. He recently thought he was having a heart attack. He throws up and hasn’t slept for weeks. He goes there against every instinct and can’t believe she sends him off to score smack. She offers him two pills. She might as well give him a bottle of scotch and a gun so he can blow his head off. She then gives him twenty lorazepam.
They’re surveilling a major transaction of microprocessors. Ellerby emphasises that they’re after Costello. All cell phone signals are under surveillance. Colin discreetly operates his phone from his pocket. He messages “no phones”. The cameras identify Costello, French, Fitzy, Delahunt and new guy, Billy Costigan.
Costello’s men turn off their phones. Dignam wants to know why. Queenan says the buyers are there, but refuses Ellerby direct contact with his undercover.
The deal proceeds and cars leave. Ellerby suspects they’re empty. He angrily criticises the surveillance team for shoddy camerawork.
Billy says there’s a rat in Dignam’s unit. Costello knew about the cameras. Billy suggests they disinform. Dignam should only tell the SIU, then see if it comes out on Billy’s end.
A distorted voice tells Madolyn to put Colin on the phone. Costello tells Colin he should earn the right to keep seeing her. Costello thinks there’s a cop in his crew. Colin needs intel on everyone at the exchange. Social security numbers, information so Colin can check it out.
Costello wants everyone’s real name, social security and bank account numbers. They should give these details and wait. Fitzy writes “Cittizins” with a double “t” on his envelope. Billy corrects him and leaves.
Billy’s instructed to follow the envelope. Colin’s at a porno cinema meeting Costello. Billy’s watching. Colin’s gotta find the guy Costello has in the department. Effectively, he’s looking for himself.
Billy should get a visual ID on the suspect. Costello hands Colin the envelope. When Colin leaves, Billy follows him. He’s told to make the arrest. Colin accidentally stabs an innocent man to death, then notices he’s on CCTV.
Costello tells Billy he has a rat in his outfit. Billy says Costello accuses him once of dishonesty, he accepts it. Costello accuses him twice, he quits. Costello’s seventy years old. One of his guys is gonna one day pop him. Billy says it must be someone who thinks they can fill his shoes. Regarding the pedigree information, French says next time, Billy should obey him.
Queenan says Colin should follow Costello to find the rat. Billy calls Queenan saying Costello’s using all new guys for something. Billy wants Costello followed, wanting to see Queenan soon.
Costello asks Colin if he heard anything about drugs, new guys or Gloucester. Colin says no. Costello’s reassured Billy’s not the rat. Colin requests surveillance on Queenan, painting him as the rat. They get Queenan’s location. Billy tells Queenan to go to 344 Washington.
Queenan meets Billy on the roof. He tells Queenan Costello has dope coming in. Costello’s twitchy and is losing his mind. Billy thinks Costello will soon kill him. Colin calls Costello saying Queenan’s meeting the rat right then. Queenan promises to release Billy soon.
Delahunt tells Billy they’re gonna find the rat. He’ll meet Billy at 314 Washington. Queenan was followed by Costello’s people. Costello’s cop tipped him off. The police tail sees Costello’s men arrive heavy-handed.
Billy takes the fire escape down. Fitzy and Delahunt arrive and ask Queenan where his boy is. Soon after, Queenan’s body lands floors below on the street. Fitzy angrily asks Billy where he’s been. Colin’s team starts shooting and Costello’s men drive off.
Ellerby wonders why Queenan went into the building. Dignam asks why Colin’s men were following him. Colin wanted Queenan followed and his reasons are classified. Dignam attacks Colin.
Colin thinks Queenan got killed by his own undercover. Ellerby wants to see Queenan and Dignam’s files. Ellerby’s Dignam’s new boss. Soon, Ellerby gives Dignam two weeks with pay. Ellerby then refuses Colin the codes.
Billy tells Fitzy he had no signal. When he got a signal, he got the call. Delahunt’s badly wounded. Delahunt knows Billy’s the rat because when he called Billy, he gave the wrong address, but Billy still arrived at the right one. Delahunt then succumbs to his wounds.
Colin calls the last number from Queenan’s phone. Billy’s phone rings. Both men are silent, then Billy hangs up. He calls the number back. He asks who he’s speaking to. Colin acts relieved. He says it’s Sergeant Sullivan, new head of Queenan’s unit. Billy’s told Dignam’s unavailable. Colin wants Billy to come in. Colin then discovers Costello’s an FBI informant.
Colin tells Ellerby Costello knows he’s being followed and that Queenan’s guy called Colin when he discovered Queenan was dead. He tells Ellerby he knows where Costello’s going and what he’s doing.
Billy texts Colin they’re going to the warehouse Costello owns. Inside a cargo container is a heap of wrapped cocaine. Costello orders the cocaine be loaded. Billy separates from the main group. Police arrive as French and Costello are leaving.
French soon shoots himself in the head. Costello makes a phone call and a phone rings nearby. Colin accuses Costello of being an FBI informant. Costello freely admits to it. Colin asks if Costello’s given him up, then Costello opens fire. Colin kills Costello and declares to his colleagues what he’s done.
Billy finally comes in. Colin will be recommending him for the Medal of Merit. Billy just wants his identity back. Colin promises he’ll arrest the rat in the building. Colin asks if Costello ever mentioned the rat he had in the police.
Billy just wants his money. Colin gets Billy’s password and leaves the room. Billy spots the “cittizins” envelope and leaves. Colin returns to see the envelope disturbed, then erases Billy’s file.
Billy gives Madolyn something to hold for him. She should open it only if something happens to him or if he calls and asks her to open it.
Then, Madolyn finds a parcel from William Costigan. There’s damning audio of Costello consorting with Colin. Colin appears and Madolyn locks herself away. Colin calls the number given. Costello recorded everything, keeping the tapes with his lawyer. Billy still wants his identity back. They soon meet.
Billy holds Colin at gunpoint and ‘cuffs him. Colin claims Costello was his informant. He’s erased Billy’s file and dares Billy to shoot him. Brown then arrives, holding Billy at gunpoint. Brown was specifically summoned because Brown knows who Billy is. Billy says Colin’s Costello’s rat and Billy has plenty of evidence. Colin still taunts Billy. Then, alone in the lift, in a complete reversal, Colin asks Billy to just kill him.
At ground floor, Billy’s executed. Brown, also. Another of Costello’s rats uncuffs Colin saying it’s just the two of them now. Colin kills this man, wipes down the gun and leaves.
Colin provides a clever explanation, recommending William Costigan for the Medal of Merit. Colin returns home to find Dignam with bags over his shoes. Dignam executes Colin. Looking at the Beacon Hill state house, a rat hurries along the windowsill.
Starring Leonardo Di Caprio. Matt Damon. Jack Nicholson. Rated 18. Dir Martin Scorsese. Released in the UK 2006. Runtime 2hrs 31mins
