Black Mass is a crime drama film based on the true story of notorious Boston gangster Whitey Bulger. Benedict Cumberbatch portrays Billy Bulger, Whitey's younger brother and a prominent politician in Massachusetts. The film delves into the dark and violent world of organized crime, showcasing the complex relationship between the two brothers. Cumberbatch's performance as Billy Bulger is nuanced and compelling, adding depth to the film's narrative. Black Mass is a gripping and intense crime thriller that highlights Cumberbatch's versatility as an actor.