In the fiercely modern, anglobalised Hong Kong, on Asia's cusp with young America and old Britain, where the cops intersperse Cantonese with phrases like yessir and sorry and a police funeral comes with the skirling of a piper, this blistering thriller packs an almighty punch.
It combines exhilarating action with liquid-nitrogen existential cool, gleaming and shimmering with the city's glass and steel. When going to the movies can seem like a pretty earnest business, it's good to have one that gets you hugging yourself with excitement.
Infernal Affairs hangs on the operatic confrontation of cop and villain that feels a little like the great De Niro-Pacino face-off in Michael Mann's Heat. But for my money, it's got something more elusive and complex than Mann ever achieved.
Tony Leung, one of the most sympathetic, attractive presences in Asian cinema, plays Yan: for 10 years, he has been a deep-cover police mole in the triads, immersed in their culture for his entire adult life, and certainly long enough to endure a hellish crisis of identity.
Yan has risen to be the most trusted lieutenant to thuggish gang boss Sam (Eric Tsang). He began this appallingly thankless task as a bright, observant 18-year-old cadet, and his recruitment was camouflaged by being publicly thrown out of training college in disgrace and then run in secret by his hardbitten chief, Superintendent Wong (Anthony Wong), the only man who knows his identity and who refuses his increasingly desperate requests to be brought in.
But there is a triad mole in the police. Andy Lau plays Ming, a cadet from Yan's graduating class, who secretly reports to Sam, sabotaging all the police swoops on Sam's cocaine deliveries. And when the police suspect a mole in their ranks, it is Ming who is approached by the Internal Affairs bureau to find the culprit. This natural born killer embarks on some character-assassination: suggesting that it is Supt Wong who is the corrupt cop.
To add to these delirious, headspinning ironies, both men have unusual domestic situations. Lonely Yan suffers from insomnia and discovers that the one place he is able to sleep is on his psychotherapist's couch: an expensive arrangement to which this beautiful, female analyst drolly consents.
Ming has moved into a spiffy apartment with his fiancee who is a writer, working on a novel whose leading character suffers from multiple-personality disorder. She is covertly basing him on Ming, never guessing just how much of the truth she has intuited. It is a pleasingly elegant and playful invention.
The two men meet face to face at the very beginning and end of the picture: when Ming buys some stereo speakers from Yan, at one of Sam's "front" businesses - and then in the thrilling rooftop finale.
This movie carries the DNA of undercover thrillers like Serpico, French Connection, Donnie Brasco, and the dual influence of Ricky Lam's City on Fire and Tarantino's Reservoir Dogs. But the emphasis contrived by director Andrew Lau and screenwriter and co-director Alan Mak is not on violence but on the cat-and-mouse business of outsmarting the enemy and the paranoia of not knowing who the enemy is - within and without - and not knowing how far to push any victory without compromising your inside source.
Tony Leung has revealed in interviews that Alain Delon is an influence on his acting style - and his face really does have that sensitive, dreamy, yearning quality which his wispy facial hair is inadequate to conceal. Of the two men, he looks younger, even boyish.
Andy Lau is quite different. The face of Hong Kong's biggest action star is extraordinarily sharp and fierce, almost feral, with eyes, nose and chin formed like some kind of nunchuck or martial arts weapon. When he smiles, he looks like a character from a manga comic or computer game, grinning with implacable and malign certainty. How curious then that it is his character which evolves more unreadably than Yan's and it is Ming whose ambitions are to make such a quantum leap.
The opening credits have a 007-ish clamour, and Eric Tsang would make a terrific Bond villain, especially in a scene where he addresses his own "graduating class" of corrupt police cadets. But the movie's allusions to Buddhist visions of hell, and the residual British empire still lingering in Hong Kong's gleaming cityscape, for me had the tiniest and most unlikely batsqueak of Le Carré, whose fallible, traitorous heroes were reputedly inspired subconsciously by Le Carré's father's rackety life as a confidence trickster and jailbird.
Yan and Ming come from backgrounds in which serious self-examination and self-knowledge are as impossible as unaided human flight - witness Yan dozing on the analyst's couch - but they are nevertheless creepingly aware that they have each built secret careers betraying the people with whom they have grown up. More importantly, they are aware of each other; the existence of each is a mirror in which they glimpse their own life-long anxiety and deceit.
All this unease and discontent is dammed and channelled into action. Sam cheerfully declaims a Thomas Campbell line to his troops: "What thousands must die so Caesar may be great!" But there is no Caesar here, no master of empire, just minor potentates ruling an unstable bipolar turf with its black economy of police snitches and corrupt cops.
Infernal Affairs is a gripping thriller with grandstanding drama, muscle-clenching suspense and two great action leads in Tony Leung and Andy Lau.
