Photo By Warner Bros. Entertainment

Listen here, kid: Leonardo DiCaprio and Jack Nicholson star in The Departed.

After directing two massive historical epics (Gangs of New York and The Aviator) Martin Scorsese approaches screenwriter William Monahan's polished adaptation of the Hong Kong police thriller Infernal Affairs with an exhilarating fluency that combines flawless visual compositions and informed musical cues with an unbridled sense of dark humor. Monahan reconfigures the setting of the original story to take place during the '80s-era battle between the "Staties" and Boston's Irish mob.

Leonardo DiCaprio plays Billy Costigan, a rookie undercover cop in South Boston, where he infiltrates the Irish mob run by Frank Costello (played with volcanic energy by Jack Nicholson). Billy's problem with maintaining Frank's unraveling do-or-die-trust escalates while he attempts to uncover the identity of Frank's secret mole, Colin Sullivan (Matt Damon), inside the Special Investigations Unit of the police department under the cool-headed Captain Queenan (well played by Martin Sheen) and his hard-ass assistant, Sergeant Dignam (Mark Wahlberg).

Billy and Colin are opposite sides of the same coin. Each man carries intense internal struggles with his peculiar demons. Colin is profoundly loyal to Frank for mentoring him since childhood in the ways of Boston's mean streets and is sharper than a laser-cut emerald for the education. He's on the "fast track" within the Special Investigations Unit, even if the canny Dignam neither trusts him nor treats him with anything less than over-the-top hostility.

Some of the movie's best laughs come from the intentionally irreverent and crude Bostonian humor shared by Boston natives Damon and Wahlberg. Inside The Departed's unity of opposites is a classic race against time scenario wherein two similar yet different men must bring down the other before those close to them discover their particular ploy. The two actors share an entertaining mix of similarities and differences that add a layer of character-driven substance to Scorsese's already dense cinematic cocktail.

The secretly impotent Colin tells his police psychiatrist girlfriend Madolyn (Vera Farmiga), "Honesty is not synonymous with truth." It's a defiantly hypocritical viewpoint that defines the philosophy of the Bush administration and de facto the attitude of a country so immured in corruption that it can't fathom the depth of the crisis.

Scorsese smuggles in some other subtle social commentary when Billy says, "It's a nation of rats." The rodent imagery haunts the film's artistic tableau that comes on the heels of an unthinkable spree of intensifying brutality.

The Departed involves interconnecting moral, ethical and physical crises that are passed along like rats spreading rabies. Nearly every character, with the exception of Queenan and Dignam, are infected with betrayal. As the only female character in the movie, Madolyn sets the bar low on her ideals of marriage and career when she furtively dates Billy, her tightly-wound psychiatric patient, in order to satisfy physical needs not being met at home with Colin. She soon becomes pregnant, and the filmmakers plant a soft question about the true identity of the child's father.

The subtextual matter of fatherhood is addressed in several different pairings throughout the story. Frank is a central father figure to both Colin and Billy. He can't help lording his barely concealed violent nature over them because he's used to scaring people into submission. Nicholson taps into his great big bag of inspiration to create an unforgettable movie gangster that is at once colorful, pragmatic and energetic.

At the other end of the spectrum is the tightly knit duty-bound relationship between Queenan and Dignam. Sheen (Queenan) sets an unruffled example that Wahlberg's character (Dignam) appropriately ignores. These are men who aspire to greatness within the context of their duty-bound jobs and whose priorities don't overlap.

There's no reason to compare The Departed to Scorsese's other gangster films, Mean Streets and GoodFellas, just as comparing those two films is an exercise in futility. Scorsese has continued to grow as a director. He tosses in an homage to a film like The Third Man to give audiences a reference point about things that please him. But he's also insanely interested in making sure that the composition of every frame contains exact pieces of narrative information and a visual balance.

He's still using the camera in new ways that complement the progress and tempo of a scene. Cinematographer Michael Ballhaus -- whose half-dozen previous Scorsese collaborations include After Hours, GoodFellas and Gangs of New York -- does an outstanding job, as does the director's ever-precise editor Thelma Schoonmaker.

Scorsese is a master director in every sense of the word, and with the help of his ensemble cast and a rousing triple-climax ending The Departed is masterpiece of modern cinema. Grade: A