Wow. I'd seen Andrew Lau's Stormriders and was not impressed--big-budget fantasy with plenty of dull CGI effects. This one, though...
Infernal Affairs, based on a script by co-director Allan Mak and Felix Chong (who also wrote the ho-hum Tokyo Raiders), represents what I'd say is both a quantum leap and a high point for the writers and directors involved--is possibly the first Hong Kong action film I've seen that turns on a tightly written, genuinely exciting plot, with a royal flush of fascinating performances.
The premise is interesting enough: a cop goes undercover and joins a triad gang; a triad member does likewise with the police force. Ten years later, they're brilliant, up-and-coming officers given the fateful assignment of hunting down and capturing the moles in their respective organizations.
It's the ultimate cat-and-mouse game, where the Hong Kong flair for virtuoso action choreography is set aside in favor of quietly intricate thriller setpieces, and matters of life and death are raised and settled by something as simple as a beeper message, or a cell phone's ring.
Part of what makes the film so compelling are the performances: Eric Tsang brings belligerent energy to the gang lord Sam; Anthony Wong is nicely understated as Police Superintendent Wong (they have a wonderful scene in an interrogation room where they taunt each other about each others' moles); Andy Lau, looking like a Chinese Harvey Keitel, brings shades of subtlety to his Judas of a police mole and does his level best to take over the picture--which, despite Lau's efforts, ultimately belongs to Tony Leung as the gang mole.
If there is a flaw to the film, it's that the parts the moles play aren't really symmetrical: Leung's is the flashier, more dramatic character, what with his sense of loss and alienation from all the things he values most (the most poignant gesture in the film may be the hidden salute he snaps at the passage of a fallen officer's funeral parade).
Lau's character is less showy, is perhaps a shade undermotivated (we don't completely understand why he decides what he ultimately decides), but there are moments of delicious ambiguity to some of his scenes, where you aren't sure just what dangerous game he's playing.
The ending has a voiceover narration and final plot twist that I found unnecessary--it didn't have the taut introduction and sudden spin into all kinds of unintended consequences that all the other twists had--but that's a rather minor complaint for what looks to be an almost flawlessly plotted film.
Andrew Lau doesn't have the distinct visual style of John Woo or Ringo Lam (you particularly miss the visual clarity or thrill those directors could bring to the one big gun battle in the film), but he's after different fish to fry: more tiny shifts in mood than operatic displays of grand emotion (like Woo at his most flamboyant (The Killer; Hard Boiled; and his masterpiece Bullet in the Head) does); more complex chess moves between intelligent opponents than complex character portrayals (like Lam at his best (Prison on Fire; City on Fire) does). Still, a wonderful film, one of the best from Hong Kong commercial cinema in a long time.