根据纪实文学《黑弥撒：FBI和爱尔兰黑帮不光彩合作的真实故事》改编。 詹姆斯·巴尔杰是全球十大在逃通缉犯之一，他发迹于波士顿，获奥斯卡最佳影片的《无间道风云》中的黑帮大佬就有他的影子。巴尔杰建立的“冬日山岗帮”（Winter Hill Gang）是波士顿著名的黑帮组织，从贩卖毒品到倒卖军火无恶不作，另外他们和包括爱尔兰共和军在内的北美及欧洲许多主要的犯罪集团都有联系。Based on a true story of James "Whitey" Bulger, an Irish Mob godfather and FBI informant who had a "secret trading" deal with his brother, William "Billy" Bulger, a state senator and a Boston public figure, and John Connolly, an FBI agent. They planned to take down the Italian mob and mafia in Boston, which went awry and things turned massively violent. When the credence for each other began fading out, drug dealing, murders, and extortion started to rise, and forced the FBI's Boston office to confirm that Whitey Bulger was one of the most notorious criminals in US history and also one of the FBI's Ten Most Wanted List criminals.
