Leonardo DiCaprio is Billy Costigan, a young cop who grew up on the fringes of crime, who goes deep undercover as a petty hood to infiltrate Frank Costello's (Jack Nicholson) crew. Matt Damon smears his clean-cut nice-guy image as Colin Sullivan, a cocky, bold, and despicable Mob soldier who becomes a Statie in order to penetrate the police investigation into his boss, Frank Costello (Jack Nicholson). Nicholson is only slightly off the rails as a brutal but savvy Mob chieftain who trusts no one.
Obviously, the "cop goes undercover and begins to lose his grip" storyline is very very old and overdone, but the addition of Costigan's opposite, the mole Sullivan, opens all sorts of exciting dramatic possibilities, which Scorsese exploits to maximum effect. It's hard enough to go undercover for the cops or the crooks, but when each side knows there's a rat amongst them, that makes it even harder. On top of that, they each need to leak information to the opposite side, sometimes in plain sight. During a high-stakes stolen-goods sale, Costigan is texting tips to the cops on the deal, while Sullivan is texting warnings to Costello. In the keystone dramatic highlight, Sullivan sends detectives to "tail" Captain Queenan (Sheen), in the hopes that Queenan will lead Sullivan to the undercover cop (who is Costigan, but Sullivan doesn't know this). Once Sullivan discovers where Queenan is meeting the undercover cop, he tips off Costello's crew, who descend on the location in order to kill the rat. At the same time, the mob crew calls Costigan to order him to participate in the killing of the rat, who is himself.
The supporting cast was chock full of talent, including Martin Sheen, Mark Wahlberg, and Alec Baldwin as fellow Staties, and Ray Winstone and Mark Rolston as Mob soldiers. Special recognition goes out to actress Vera Farmiga as the state psychologist Madolyn, who engages in an affair with Sullivan and a tryst with Costigan. I read a profile of Farmiga in the New York Times Magazine, and I expected a second-rate Cate Blanchett, but Farmiga was refreshing and engaging as Madolyn, and she tempered her exotic looks (unearthly blue eyes and translucent pale skin) with a bad haircut and a passable Boston accent. The Boston accents ranged from impeccable (Damon and Wahlberg) to quality (DiCaprio, Baldwin, Sheen), to occasional (Nicholson).
Kudos also go out to the location photography, especially the under-the-Red-Line meeting with Costigan.
If this weren't Martin Scorsese, it'd earn an A+ grade, but the songs and score were an uncharacteristic weak point, so it earns a straight A. (Regal Cinemas Fenway)