Based on the Hong Kong blockbuster, "Infernal Affairs," this story is about a cop who goes undercover in the mob. At the same time, the mob places one of their own on the police force as a mole.

In this version by Martin Scorsese, the scene shifts to Boston, where mob boss Frank Costello (Jack Nicholson) puts loyal-from-boyhood employee Colin Sullivan (Matt Damon) through police training. As Sullivan rises through the ranks, Special Investigations chiefs Queenan (Martin Sheen) and Dignam (Mark Wahlberg) recruit rookie Billy Costigan (Leonardo DiCaprio) to get "kicked off" the force and do time to gain Costello's confidence. Costigan is soon entrenched in Costello's gang, texting messages back to his police bosses.

All of that happens before the opening titles, so you know you're in for a wild ride. Costello's casual racism (it takes less than five minutes for him to tell us what he has against black people) underscores the mistrust that permeates not just his world, but the cops' as well. An encounter with a bunch of Chinese gangsters takes this to nationalistic levels, with Costello raging on about how we do business "in this country." Scorsese gives Nicholson wide berth, and he takes it and runs.

Providing a romantic interest for both Sullivan and Costigan is police therapist, Madolyn (Vera Farmiga). She's charmed by fiancé Sullivan's wit (from a crime scene, he calls her to say, "I saw a dead guy. I think I'm having post-traumatic stress. Can I see you for lunch?"), but also troubled by his deceit and occasional displays of aggression. At the same time, she's touched by Costigan's vulnerability and moral integrity.

THE WRAP-UP: This is, by far, the best movie of 2006. It's classic Scorsese, with characters so engaging and a storyline so twisty-turny, just plan on seeing it twice. DiCaprio and Damon are as solid as ever, but Wahlberg is the real scene-stealer, with dialogue so abrasive, it sets a new standard for gritty cop characters. Alec Baldwin, as the head of Sullivan's unit, chews whatever scenery Wahlberg misses.

Make no mistake, though. This is Jack's world and everyone else is just window dressing. When told by an associate that his mother is "on the way out," Nicholson as Costello says, "We all are. Act accordingly." He infuses Costello with the effortless charm and maniacal glee we've come to expect from our mob bosses, but leaves room for some petty desperation, as well.

PARENTS SHOULD KNOW: Rated R for strong brutal violence, pervasive language, some strong sexual content and drug material, this movie isn't for youngsters. They're not lying when they say this movie contains all those things!