Infamous Irish gangster James "Whitey" Bulger strolls the streets of South Boston, literally, getting away with murder.

Despite numerous attempts by police, he seems strangely impervious to law enforcement.

But there is a dirty secret behind Bulger's charmed criminal existence. He is getting by with the help of a very important friend at The Federal Bureau of Investigation, a brash young agent named John Connolly.

Connolly and Bulger share "Southie" roots and for Agent Connolly, loyalty to the old neighbourhood triumphs over the fidelity, bravery and integrity he has sworn to uphold as an officer of the law.

Pulitzer Prize winning journalist Gerard O'Neill and his colleague Dick Lehr first broke the story in the Boston Globe in 1988. And penned the Edgar award winning true crime tome, Black Mass.

Together they guide us on a journey that begins in the blood-soaked back alleys of South Boston and eventually leads all the way to one of the shameful scandals in hallowed halls of the FBI.