One of the best Hong Kong films in years, Infernal Affairs has already spawned two sequels and a planned Hollywood remake. In a cinema not known for its restraint, Infernal Affairs is a complete surprise-a subtle, nuanced gangster film with exceptional performances and a gripping plot. It can stand up next to any film released this year.

Steeped in Buddhism, the film opens at a temple where a small-time crook persuades one of his gang to enter the police academy. At the same time, a cadet is chosen to go undercover into the triads. Years later, Lau Kin Ming (Andy Lau) has worked his way into a police narcotics unit, while Chen Wing Yan (Tony Leung Chiu-Wai) has reached the upper levels of a gang run by Sam (Eric Tsang).

The hot-tempered Sam has his own counterpart in the police-Wong Chi Shing (Anthony Wong), a disciplined and relentless cop determined to bring him down. Wong sets a trap for Sam, who is brokering a major drug deal. When Sam is tipped off beforehand, Wong realizes he is dealing with a mole in his force. He pressures Yan for information, knowing that the cop is under increasing scrutiny from his paranoid crime boss.

Infernal Affairs plays out as a series of increasingly edgy confrontations that place both Yan and Lau in extreme jeopardy. Directors Andrew Lau and Alan Mak stage each encounter with a sense of brinksmanship that is breathtaking. When one side pushes too hard, resulting in a horrific death, the lives of both cop and mole begin to unravel.

For those accustomed to a Hong Kong of bullets and kung fu, the action here will be disconcerting. Violence is kept to a minimum, and the chases are more mental than physical. But once the story is set into motion, the tension is relentless. It helps that the directors are working with the cream of Hong Kong actors. Tony Leung Chiu-wai offers a strikingly complex portrayal of a cop at the end of his rope, confining almost all of his playing to finely calibrated reactions to other characters. Tsang, usually seen in light comedies, gives a commanding performance as a suspicious gangster. He's matched by Wong, who finds a quiet authority within his difficult role. Andy Lau, one of Hong Kong's most prolific actors and pop stars, digs into his part with relish, developing a villain of Shakespearean proportions.

Cop thrillers don't come much more polished, or enjoyable, than Infernal Affairs. That may be why Martin Scorsese will be directing Leonardo DiCaprio and Matt Damon in the remake. Here's hoping the original does well enough to justify the stateside release of its two equally intriguing sequels.

-Daniel Eagan