Great artists do more than express emotion; they also invent it. The difference comes through most clearly when there’s no subject matter to distract you–when you listen to Beethoven and Chopin, for example, or Armstrong and Coltrane, and hear how they called up ranges of feeling that were new to the world. But you can just as well experience this opening of emotional territory when you look at a Velázquez painting, or read Dubliners, or watch a sequence of classic filmmaking.

Here’s something of the mood that Martin Scorsese invented: The Rolling Stones churn and rumble and keen on the soundtrack as the camera cruises like a vintage Chevy into a low-ceilinged urban storefront. You take in all at once an atmosphere of shadows, tribalism and menace; you sense the directorial momentum, as if the engine that drove you inside had been left running.

Scorsese introduced this feeling many years ago, in Mean Streets; but since then he has ventured far from the Little Italy that served as a platform for the emotion. He went to Las Vegas and Tibet, 1930s Hollywood and ancient Judea, testing and stretching himself as great artists do. In so doing, he left behind the mood that was initially so striking, and so peculiarly his. I thought it was missing even in GoodFellas. I hadn’t expected to encounter it again.

Yet here it is once more, revived for two and a half hours nonstop in The Departed. You might be surprised that Irish Catholic South Boston should have provided the opportunity for this stunning return, but I tell you the range of emotions would be characteristically, authentically Scorsese’s even if The Departed were set in Kowloon.

Which, in a sense, it is.

Sources close to the production inform me that Scorsese was initially reluctant to direct The Departed, since this producer-initiated project is a remake of the Hong Kong thriller Infernal Affairs (2002, directed by Andrew Lau and Alan Mak). Fans of Infernal Affairs (who are many, like the sequels) know it to be a clever, stylish, fast-moving and superficial action movie focused on the game-playing of two men who lead double lives. One, known to everyone as a police detective, works secretly for a mob boss. The other, known to everyone as a gangster, works undercover for the police. How these two deceivers chase each other through Infernal Affairs is far more important than anything they might feel during the pursuit. The characters’ one or two moments of obligatory heartsickness do nothing to disrupt the picture’s conventional sentiments of loyalty toward elders, chivalry toward women, fraternal respect toward a worthy adversary.

To Americanize this story, the producers of The Departed (who are also many) handed a translation of the script to screenwriter William Monahan. With considerable energy and a great trust in the power of foul-mouthed insult humor, Monahan went about transposing the events and characters to South Boston, a milieu he evidently knows something about. (I take it on faith that his grandfather was not originally a Manischewitz.) This package then went to Scorsese, who might have turned it into a mannerist exercise, like Cape Fear, but instead directed the movie as if every moment meant life or death, not just for the characters but for himself.

Start with the voice: a low, rattling sound, at once angry and mocking, that introduces the story of The Departed with a patch of seemingly omniscient narration. Later, when this frightening noise issues from an identifiable character, someone will guess that the speaker suffers from throat cancer. But nothing is truly eating this man, except the acid of his own amoral power. The voice belongs to mob boss Frank Costello (Jack Nicholson), who very soon will be a player in the drama but who for the first crucial moments of The Departed figures more as the genius loci of South Boston.

Images as ragged as the voice–shaky, fuzzy, archival–accompany his opening words, showing you the street fights that broke out in this neighborhood during the school-integration struggle of 1974. Then Costello himself steps onto the screen in devilish silhouette, a lean and stooping Spirit of South Boston, with long hair sweeping back from the forehead and a scraggly beard pointing down from the chin. Costello will prove to be an artist of sorts, a social philosopher, even a mentor; but he is first of all a man who rules by torture and murder, which leaves him looking none too clean. Like the people who attacked the school buses, he prefers his neighborhood to remain as it is: his own private hell, where “I beg your pardon?” is registered by smashing a beer stein against somebody’s skull.

I must immediately deny that this representation is faithful to the lives of South Boston’s good citizens. Nor do I think that Scorsese means it to be perceived as factual. Like Clint Eastwood, who turned Somerville into a surrogate Wild West town in Mystic River, Scorsese is working within a genre–though in this case the conventions are loose, since the director himself established them. The genre of the Scorsese picture can be open in form, as it was in Mean Streets (which an Italian-American friend once described to me, with fervor, as “the greatest documentary ever”); or, by contrast, it can be a closed system, as it is in The Departed, where the emotions and themes play out entirely within Scorseseland. You may, as a result, rate the present movie lower than Mean Streets; but then, understanding the nature of the game, you may also want to allow Scorsese his conceit, and Frank Costello his Mephistophelian allure.

He’s the only character who’s free to enjoy himself, you see, and so he stands apart from the two main protagonists. These are Costello’s mole within the State Police and the State Police mole within Costello’s mob–men who must never show their true feelings, and so are played, respectively, by Matt Damon and Leonardo DiCaprio. While Nicholson, the great cat-tearer, is busy tattering his every scene, Damon and DiCaprio keep their energy contained, suggesting far more than they show. Damon’s chief asset here is that wide, ingenuous grin, which proves, on closer inspection, to be a cold apparatus for sifting and swallowing. Rising emotions bump against it and sink back down; lies filter through; and all the while nothing moves on Damon’s face, except for a passing shadow. DiCaprio, by contrast, relies for effect on his level, hot-eyed gaze and a chronic tightness at the top of his throat. Though he, too, conceals and controls everything, he must at times appear to act on impulse (as when, like any credible Southie gangster, he beats the crap out of someone). Prescription drugs help him maintain the imposture; but the simultaneous expression of adrenaline and suppression of self sometimes leave this man in a state of quivering immobility.

When DiCaprio shows up, unannounced, at the door of his love interest, neither entering nor leaving, neither volunteering anything of himself nor asking openly for anything from her, she gapes at the glowering, hard-breathing figure and says, “Your vulnerability is freaking me out right now. Is it real?”

He takes a moment to consider the question, then replies, “I think so.”

What makes The Departed so wrenching–far more than the tension of the plot or the abundant violence that provides its release–is the terrible honesty of this answer. The man might actually want to be vulnerable, just for a moment–he might even approach an admission of vulnerability. But by this point he’s entangled so completely in lies that he doesn’t know for sure, and neither do you. Few of us face situations as extreme as this character’s, yet few will fail to recognize the confusion. On that level, it doesn’t matter that The Departed is a closed system. Scorseseland is true to people’s minds and hearts as we know them.

On the sociological level, though, The Departed does suffer from its self-enclosure. The woman to whom DiCaprio has come in his hour of need is a police psychiatrist, played with resourcefulness, valor and a vested gray suit by Vera Farmiga. Whether she deserves an Oscar nomination or the Bronze Star I can’t say, but Farmiga makes what can be made of the character, who through wild coincidence (and a shocking inability to say no) winds up in bed alternately with Damon and DiCaprio. The women in Infernal Affairs were no stronger as characters, but at least there were two or three of them. Can there be, in all of Boston, only one woman to soak up all this suffering? The contrivance may not bring down The Departed, but it does expose the movie’s walls as being shakier than they should be.

Matt Damon and Mark Wahlberg (as a detective sergeant) may bring genuine Boston accents to the movie; Martin Sheen (as DiCaprio’s true boss) may add the weight of his Irish Catholic gravity; but this is ultimately just ornamentation, like the inconsequential subplot that worsens Costello’s already unforgivable corruption. It doesn’t matter that this latter complication is based on events that actually happened in Boston. The Departed was filmed in Massachusetts, but it is set wherever boys trade their lives for an armful of groceries, and men suffer their bones to be broken rather than risk being called fags or pussies. This is not a specific location–not anyplace capable of being documented–but it’s real enough.

It’s also a place that’s essentially cinematic. You see that especially when the mannerist in Scorsese takes over, and he begins paying homage to Infernal Affairs. In one sequence, he copies (and outdoes) Lau and Mak’s fast, nervous pans and multiple setups; in another, he sets the action as close as he can to Hong Kong, in Boston’s Chinatown. You might even read one key event in the story as a filmmaker’s allegory: A police operation fails because the technicians didn’t install enough hidden cameras, leaving the director (that is to say, the officer in charge) to rage about not getting his coverage. In recent years, when Scorsese has inserted such knowing little touches into his movies, they have seemed to interest him more than the story itself. In The Departed, they’re always absorbed into the relentless, compelling flow.

It’s not just DiCaprio’s character who is put into a state of trembling immobility. For the entire running time of The Departed, I felt adrenaline pumping through me and yet could neither fight nor flee. I could only watch, in amazement and admiration. And when the movie ended and the credits rolled, I remained stuck to my seat. I wanted a little time, before I tried walking, for my heart rate to go back down.