Martin Scorsese's remake of the Hong Kong thriller INFERNAL AFFAIRS (2002) is a thrilling return to form, a psychological gangster film whose diabolically convoluted premise follows two men living double lives, their manufactured identities sustained by a web of lies that simultaneously keeps them alive and strangles their souls. Colin Sullivan (Matt Damon) and Billy Costigan (Leonardo DiCaprio) grew up in the same tough South Boston neighborhood, each in the shadow of Irish mob boss Frank Costello (Jack Nicholson, only rarely lapsing into "Here's Johnny!" mannerisms). But while Costello took the orphaned Colin under his wing, schooling him in the ruthless, bottom-feeding code of the streets, Billy was sheltered from Costello's pervasive corrupting influence by his father, the one law-abiding member of a mobbed-up family. Both entered the Massachusetts State Police academy, and each enters an elite division of the force: Colin, the very image of a bright, incorruptible cop, joins the Special Investigations Unit, which is mandated to bring down Costello's empire by any means necessary. Colin ostensibly reports to Captain Ellerby (Alec Baldwin), but is in fact Costello's inside man, keeping his mentor apprised of every move the police make. While still a cadet, Billy is tapped by avuncular Captain Queenan (Martin Sheen) and foulmouthed Southie Sergeant Dignam (Mark Wahlberg) to work in an ultra-secretive undercover division. Billy's chief qualification is his family's criminal history, particularly his late Uncle Jackie's close relationship with Costello; after Queenan and Dignam arrange his expulsion from the academy and a stint in jail, Billy is perfectly positioned to worm his way into Costello's organization and feed information to the police. The two moles soon become aware of each other's existence, but neither knows the other's identity or that they're connected by therapist Madolyn Madden (Vera Farmiga), who's dating Colin and counseling Billy as a condition of his parole. Hidden behind their masks and under ever-escalating pressure to root out the traitor within their respective organizations, Colin and Billy both begin to crumble. William Monahan's screenplay hews remarkably closely to Alan Mak and Felix Chong's convoluted original (though their names are buried in the end credits), but Scorsese makes it his own, from the vivid pop soundtrack to the seething paranoia and spasms of brutal violence. The cast is uniformly excellent, with Ray Winstone a standout as Mr. French, Costello's red right hand.