But I was wrong, and in particular about Damon and DiCaprio. This isn’t merely a cunning sprint along the knife edge between cops and mobsters, one that spooks you into feeling at any moment that you might fall off, or worse, get cut for standing too long in the dangerous middle. It’s also the smartest kind of spectacular that an international remake can be: it picks up the clever threads of story from its source material and weaves them into another world in such a way that it’s hard to see how they didn’t spring from that world in the first place. The Irish working-class cultures of Boston’s law-enforcement agencies and criminal underworld are as much characters in The Departed as the actual cops and mobsters themselves. Watching Infernal Affairs and trying to imagine such all-American boys as Damon and DiCaprio in roles inherently Chinese -- with a whole different ethos about machismo -- led me to despair. With screenwriter William Monahan’s (Kingdom of Heaven) whole-cloth transmutation of the basic story into something that feels as if it sweated itself up off the mean streets of Beantown, they couldn’t be more perfect.

You have to wonder whether Scorsese has found his next-generation DeNiro, his new muse/alter ego, in DiCaprio -- Gangs and Aviator almost feel, in retrospect, like warmups for their onscreen-offscreen give and take here. DiCaprio’s Billy Costigan, a rookie state cop gone deep undercover in the Irish mob, is the kind of character DeNiro would have played 30 years ago, a young man driven by a rage kept barely in check by the constraints of police honor, and DiCaprio inhabits him with a fiery intensity reminiscent of DeNiro. And Scorsese adores him, pushes in on his glower and lingers there, making love to his slow-burn. DiCaprio’s is nowhere near as showy a performance as Jack Nicholson’s (Something's Gotta Give, Anger Management) inevitably is as crime boss Frank Costello -- imagine the Godfather as played by the Joker -- but the fact that DiCaprio, as his new underling, is not blown off the screen by it is a testament to DiCaprio’s power here. In a quieter way, DiCaprio gives as good as he gets from Nicholson, which is one strand of astonishment among many in this exhilarating movie.

The biggest bit of cleverness comes straight from Infernal Affairs: not only is there a cop spying on the mob from the inside, there’s a mobster mole at state police HQ. That’s Colin Sullivan, and Damon (Syriana, The Brothers Grimm) plays him cold and calculating like he invented the idea, with an effortless bravura that keeps you questioning Sullivan’s loyalties: surely he cannot really be this bad a bad guy... can he? DiCaprio’s and Damon’s innately assured performances only add to a level of suspense that eventually becomes almost unbearable, as Sullivan’s police assignments get him closer to the goal that Costello has set for him -- rooting out the cop that the crime boss suspects is hiding in his organization -- because we’re never entirely certain where either man’s allegiance will fall when push comes to shove.

And for all the tripwire tension and even moments of sheer terror, The Departed is frequently downright comic: Nicholson, of course, can make almost anything a punchline, stealing your sympathy with it even when you want to hate him, but who’da thunk that Mark Wahlberg (Invincible, The Italian Job), as one of only two cops who know Costigan’s real identity, could be so funny in a nimbly deadpan kind of way? He takes a no-bullshit attitude and brings it all the way around to something that makes you think maybe he’s all bullshit -- in one scene that emphasizes the smart, snappy speed of Monahan’s script, Wahlberg and Alec Baldwin (Fun with Dick & Jane, The SpongeBob SquarePants Movie) as the head of a rival state-police department, trade a rapidfire barrage of vulgar insults that shoots by before you even realize that they’re both kidding... maybe.

The whole film teeters back and forth like that, never letting you settle for sure on anything, not even where your own approval belongs. It’s an electrifying experience, one that reminds us why we go to the movies in the first place.

(Technorati tags: Departed, Martin Scorsese, Leonardo DiCaprio, Matt Damon)