I think this might be my favourite performance from Leonardo DiCaprio as he takes on the mantle of undercover cop "Billy". On a perilous arms-length basis from his boss (Martin Sheen) pretty much from the start of his career, he must undergo the violent perils of prison so he can convincingly infiltrate the gang of hoodlum "Costello" (Jack Nicholson) who runs the crime syndicate in the city of Boston somewhat enigmatically. Meantime, we also meet "Colin" (Matt Damon) who is in a mirror-image position with the State police. As the situation in the city becomes even more dangerous it becomes clear to both the cops and to "Costello" that there is a fly in their respective ointment, and those men's positions become even more hazardous. Now each must try to identify the other before the entire house of cards comes crashing down in a blaze of gunfire. If we add to the mix the fiery and determined detective "Dignam" (Mark Wahlberg) and a bit of love interest from "Madolyn" (Vera Farminga) and we get an engagingly complex thriller that unravels cleverly and slowly over 2½ hours generating a proper sense of menace. Nicholson is on superb form as the maniacal boss whom you just know probably isn't trustworthy - even for those his own side, and the focussed efforts from Leo and Damon deliver well to build the tension effectively. I liked the writing - and the paucity of it. There is comedy here, there is threat here but there is very little extraneous verbiage. The characters have a visceral quality to them that, as the story develops, really does immerse you in their tawdry and shady goings-on. I can't say that I loved the ending - somehow it seemed a little bit rushed, but there's certainly vindication there for someone... This is the kind of drama that thrives by knitting the myriad of threads together without having to faff about with timelines, loops, or repetition. It's a story that evolves in a plausibly hazardous yet characterful fashion and if you can catch it on a big screen, then it's highly recommended. Scorsese - indeed, just about everyone, at their best.