At the heart of a cat-and-mouse game between gangsters and police, both sides get their information from undercover informants. But when the secret is out, a race ensues to reveal the identity of the mules.

Having served as Martin Scorsese’s inspiration for 2006’s The Departed, Infernal Affairs may seem more effective than its remake. With a running time of 1h40, the film takes on board a number of well-developed palettes, including the morals of its protagonists. Lau Kin-Ming (Andy Lau), sent as a police infiltrator by the gang, his moral values are put to the test over the course of his years in service. Meanwhile, Chan Wing-Yan (Tony Leung Chiu-wai) has been operating within gangs for the police for almost 10 years. The characters’ roles and morals are reversed, and they are torn between their original mission and their new status. Yan, although on the police, is increasingly behaving like a mobster, walking a delicate line between legality and illegality.

Andrew Lau Wai-Keung plunges us into a tense atmosphere, where every movement, phone call or hand-to-hand exchange is an essential part of the action. We become observers of these exchanges on both the police and gangster sides. Infernal Affairs’ editing quickly becomes the film’s centerpiece. By alternating between the two mules and the two sides of the operation, an omnipresent tension is created all the way to the next sequence. Dynamic yet able to slow down at important moments, Andrew Lau Wai-Keung keeps the focus on the story and the opposition between the two mules.

The performance of Tony Leung Chiu-wai and Andy Lau reinforces our investment in the plot. With their subtle interplay of glances and facial movements, the two actors carry the film together. But the rest of the cast is also up to the task, again with revealing subtlety. The clues are in the details, and like our two protagonists, we have to be alert to the smallest hints that might reveal their identity.

Infernal Affairs is never explosive; on the contrary, most of the film takes place in cold calm. Everything depends on a phone call or a discussion that can turn the tide of events. This makes the violent or bloody scenes all the more intense when they occur suddenly.

Andrew Lau Wai-Keung is like its characters, playing both sides of a blurred moral line, subtly hiding its clues only to reveal them later. Infernal Affairs knows how to play with its aesthetic style in staging, editing and sound to grab our attention and never let go.