After previewing “Black Mass” at The Harbor Theatre, my first thought was, Johnny Depp is back! And he is formidable as James “Whitey” Bulger, the notorious crime boss of the Irish mob in South Boston.

The film focuses on Bulger's dealings post prison, including becoming an informant for the FBI, based on the book, “Black Mass,” written by Boston Globe journalists Dick Lehr and Gerald O'Neill.

The film begins with Winter Hill Gang member Kevin Weeks (Jesse Plemons) sitting down with an FBI agent to spill his guts about Bulger and the gang's exploits.

As Weeks begins to sing, we are transported to the year 1975. Bulger (Johnny Depp) has recently finished serving nine years in Leavenworth and Alcatraz and is back with his “Southies.”

FBI agent John Connoly (Joel Edgarton) grew up with Bulger — he was friends with his younger brother Bill (Benedict Cumberbatch), now a Massachusetts senator — and has been reassigned to the bureau's Boston division.

Connoly's the one that comes up with the idea of getting Bulger on board as an informant. Bulger doesn't go for the idea right off; he has to think about it, come up with his own plan, and make it work to his advantage. And he does.

Seems the Italians in North Boston, OK, the Mafia, are looking to move in on Bulger's territory. Bulger figures he'll help the FBI get the goods on the “diegos” while he and his boys continue doing what they do with impunity: vending machines, racketeering, drug smuggling, bookies, and eventually skimming off the haul at Jai Alai in Miami.

Sounds like a win-win for Bulger and the FBI. But before Connoly’s boss Charlie McGuire (Kevin Bacon) agrees to Connoly's idea, McGuire tells him to swear there will be no drugs and no murders. Yeah. Right.

As Connoly says during his own interrogation, “Southies went from playing cops and robbers on the playground to doing it for real in the streets,” and that “a Southie's bond is one that never gets broken.”

Bulger is a ruthless son of a gun who takes out his own share of enemies, but John Martarano (W. Earl Brown) makes most of the hits for the gang. He and the Winter Hill Gang have a designated spot along the Quonsett River, under the bridge, where they dump bodies. It was known as the Bulger Burial Ground.

Bulger murders Brian Halloran in a parking lot in broad daylight with a shotgun – followed by a handgun – for talking to the feds about his involvement in the murder of Roger Wheeler (the new head of the Jai Alai who ordered a review of the books) and shut out Bulger.

Depp's portrayal of Bulger might possibly be his most brilliant; he's intense, intimidating, insidious. And the eyes — a kind of milkyish blue that bore right into you. The true depth of his talent, his ability to morph into any character shines, albeit in a most menacing way, particularly in two scenes.

Bulger and two other members of the gang are having dinner at Connoly's new house. He got a big promotion when the FBI brought down the north end Italians led by Joe Angiulo (thanks to Bulger), but his wife, Marianne (Julianne Nicholson), doesn't want any of them in her house. She begs off actually interacting with them before or during dinner. Bulger inquires about Marianne and goes upstairs to see her. In this scene, it sucks to be Marianne. On the surface, he's just inquiring about her health. He puts his hand on her forehead to see if she has a temperature; her face to see if she is cold, and then her neck, ostensibly checking for swollen glands — just squeezing just a bit too tightly.

Also at the dinner, he compliments John Morris (David Harbour) on the steak marinade and asks what the recipe is, Morris says its a family secret. Bulger keeps prodding. After Morris gives it up, Bulger comments on how quickly he shared a secret and wonders if Morris would give him up as easily.

The entire cast nails it — including their believable south Boston accents.

Supporting cast includes Dakota Johnson as Bulger's wife or girlfriend, Lindsey Cyr, mother of his son Douglas who dies at age 6 of Reyes syndrome; Corey Stoll as FBI agent Fred Wyshak, determined to dig into records to find out why the bureau had not busted Bulger; Rory Cochrane as Steve Flemmi, Bulger's right hand man — and the only one Bulger tells about the informant agreement.

Actually, Bulger never saw himself as an informant. He was just taking care of business.

Out of this brilliant cast, Depp is sure to receive an Oscar nomination, and, quite possibly, take home the gold.

Director Scott Cooper has created a masterpiece of a gangster film from the screenplay written by Mark Mallouk and Jez Butterworth. Don't miss the opportunity to see it on the big screen.

“Black Mass” plays at 7 p.m. at The Harbor Theatre Friday, Oct. 9 through Sunday, Oct. 11 with an additional 2 p.m. show on Sunday.

The theater is located at 185 Townsend Avenue in Boothbay Harbor.