Plot
In 1975, James "Whitey" Bulger, leader of the Winter Hill Gang, controls most organized crime within South Boston, along with his right-hand man Stephen Flemmi, newcomer Kevin Weeks, and callous hitman Johnny Martorano. Bulger lives with his longtime girlfriend, Lindsey Cyr, and their young son, Douglas.
Bulger's supremacy is challenged by the North End-based Angiulo Brothers, a rival gang that is part of the New England Mafia family. FBI agent John Connolly returns to the area, having grown up in South Boston as a friend of Whitey and his brother, Massachusetts Senate president William "Billy" Bulger.
After the Angiulo Brothers send a motorcycle riding assassin who murders a Winter Hill soldier, Whitey becomes an informant for Connolly. Connolly believes he can infiltrate the Angiulo Brothers' organization with Whitey's help. Although Whitey hates the idea of being a rat, he understands what the resultant protection would afford him, his gang, and his family. Douglas suffers from Reye syndrome, leading the devastated Lindsey to remove him from life support over Whitey's furious objections.
Although Connolly is supported by his co-worker John Morris, their boss, Charles McGuire, is suspicious. Whitey increasingly exploits his status as an informant, using Connolly's "protection" as a cover for his crimes. When Connolly demands information on the Angiulos' racketeering locations, Whitey gets pictures of the rival gang's hideouts, allowing the FBI to plant wiretaps. The FBI arrests the Angiulos, thus eliminating the remaining opposition to Whitey's power. Blinded by his past, Connolly grows closer to Whitey and the gang and even invites them to his house for a cookout. His wife, Marianne, sees negative changes in her husband as his agent-informant relationship with Whitey grows, including accepting expensive gifts and money from the gang.
An associate, Brian Halloran, fears for his own life and goes to the FBI to report Whitey's involvement, much to Connolly's displeasure. Connolly then tells Whitey of Halloran's accusation, resulting in the murders of Halloran and an unnamed accomplice. Following his mother's death in 1985, Whitey's behavior becomes increasingly violent and unpredictable, deteriorating his informant relationship. Steve's prostitute stepdaughter, Deborah Hussey, insists that she rejected any matters to attack Whitey. Believing her, they go to an apartment complex, and Whitey kills Deborah in front of Steve.
When "bulldog" prosecutor Fred Wyshak is appointed the new assistant U.S. Attorney in Boston, Connolly attempts to make friends and perhaps divert his attention from Whitey. Wyshak bluntly refuses and demands the FBI arrest him. John McIntyre, an informant within the Winter Hill Gang, informs on an attempt by Whitey to smuggle weapons for the IRA. The shipment is seized, and Whitey kills McIntyre after Connolly tips him off.
Wyshak and McGuire investigate Connolly's management of Whitey's informant role and realize most of the "tips" were obtained from other informants. Morris, disillusioned and fearing prosecution, divulges Connolly's and Whitey's relationship to The Boston Globe, and a front-page story exposes the FBI's links to organized crime. As Connolly, Flemmi, Weeks, and Martorano are arrested, Whitey gives Billy a final goodbye from a gas station pay phone before leaving Boston.
Epilogue: Weeks and Martorano, respectively, receive five- and twelve-year reduced prison sentences – both now walk free on the streets of Boston. Flemmi serves a life sentence after pleading guilty to ten murders. For cooperating, Morris is granted immunity from criminal charges in return for testifying against Connolly. Billy quits the state senate to become Chancellor of the University of Massachusetts, but is forced to resign upon discovering his communication with Whitey. Opting not to testify against Bulger, Connolly receives a forty-year sentence for the second-degree murder of John Callahan. Whitey leaves Boston in 1995, and various sightings are reported around the world. After twelve years on the FBI's most wanted list, an anonymous tip leads to his arrest in Santa Monica, California on June 22, 2011. He receives two consecutive life sentences plus five years for the deaths of at least eleven people.
