By Todd McCarthy

After too many Caribbean vacations, Johnny Depp finally gets back down to some serious business in Black Mass, a major league real-life gangster film loaded with ripely presented murders, beatings, betrayals and vengeance-takings, all backed up by a deep-secret arrangement between Boston’s top-dog criminal and the FBI. Even if director Scott Cooper’s jump into big-time studio filmmaking feels familiar and derivative in some respects, he has taken care to borrow only from the best, and a top-notch cast socks over the many dramatic opportunities. Box-office prospects look potent.

Long-time Depp fans who might have lately given up hope of his doing something interesting anytime soon will especially appreciate his dive into the deep end here to personify genuine perfidy in the guise of legendary hoodlum James “Whitey” Bulger, the crime kingpin of South Boston from the 1970s until 1994, when he was forced to go on the lam for what ended up being 16 years. For a dozen of them he was second only to Osama Bin Laden on the FBI’s Ten Most Wanted list.

What gave him such status provides the substance of this continually absorbing melodrama, one that scarcely glamorizes Bulger’s complete allegiance to a life of crime. Bulger, to this day, denies that he was a rat for the Feds, the worst thing you could be in his world; to him it was an “alliance” to rid Boston of the Italian mafia.

You can detect Depp behind the elaborate makeup job–the thinning, blondish, brushed back hair, the blue eyes, the rotten teeth. He may be better-looking than the real Bulger, but not by much. He’s far from the biggest guy in the room, but he’s plenty tough and has a Bloodhound’s sense of smell for anyone who might be thinking of crossing him. He grew up in the slums of Southie and has known most of his cronies since playground days.

In a nod to Citizen Kane, the script by Mark Mallouk and Jez Butterworth is structured around interview testimony given by some of Bulger’s longtime henchmen after their arrest and their boss’s disappearance. Their comments are revealing but not conflicting: Their boss was the thug of thugs, the baddest ass in Boston, a man who finally, in his 80s, was sentenced to two life terms plus five years after having been charged with murder (19 cases), extortion, racketeering, narcotics peddling and money laundering.

Early scenes neatly establish the tough-guy ways of Bulger, recently sprung from nearly a decade in federal prison, including Alcatraz, and his underlings in the bars and cars of Southie. An escalation of war with the Angiulo family in North Boston seems inevitable, but Bulger’s Winter Hill Gang isn’t the only organization that wants to bring the Italians down: The FBI can’t get anything on them, so the bureau’s John Morris (David Harbour) and an agent who’s known Bulger since boyhood times in the neighborhood, John Connolly (Joel Edgerton), eventually persuade Bulger that it’s in his interest, as well as theirs, to secretly team up against their mutual enemy.

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This works out brilliantly, especially for Bulger, who now not only has Boston to himself by enjoys virtual carte blanche as far as the Feds are concerned; he can extort or kill essentially anyone he wants and knows he can get away with it. Turning a blind eye toward this as best he can is Bulger’s upstanding brother Billy (Benedict Cumberbatch), who happens to be Massachusetts’ most powerful state senator.

The one thing Bulger can’t control relates to his only child, a six-year-old boy who dies from an allergic reaction to an injection. He breaks down and argues with his wife (Dakota Johnson), after which we never see her again; maybe we don’t want to know what happened to her.

Where killings are concerned, sometimes Bulger does them himself, while on other occasions he lets one of his beefy goons handle them; Rory Cochrane, W. Earl Brown, Jesse Plemons and Scott Anderson are plenty convincing as his inner-circle boys. Cooper, who previously directed Crazy Heart and Out of the Furnace after working as an actor, times and stages the violence for sharp visceral impact and street realism, avoiding operatic extremes as well as trendy fast cutting and ridiculous forms of physicality.