As Infernal Affairs opens, Ming (Andy Lau of Full-time Killer) is being initiated into the criminal underworld by triad boss Sam (Eric Tsang of The Accidental Spy), who ends his speech to his young charges by wishing them success in the police department. Ming enters the police academy, where he excels, but sees his classmate, Yan (Tony Leung Chiu-Wai of In the Mood for Love), expelled for "breaking the rules." It turns out that Yan wasn't actually drummed out of the force, but recruited by Superintendent Wong (Anthony Wong of Hard-Boiled) as an undercover operative. Just as Ming is achieving success in the police department while secretly working for Sam, Ming is gaining Sam's trust as a triad member, while reporting to Wong. Ten years later, both men, still undercover, have grown confused about their true identities, while their bosses, Sam and Wong, wage a battle of wits against each other. Each boss learns that the other has a mole working for him, and unwittingly entrusts the mole himself to ferret out the culprit. Ming and Yan scramble to expose one another's identity in an effort to save their own skins. Infernal Affairs was co-directed by Andrew Lau (who worked as a cinematographer on several of Wong Kar-Wai's films) and Alan Mak. Renowned cinematographer Christopher Doyle served as "Visual Consultant." The film was shown at New Directors/New Films in 2003.
by Josh Ralske synopsis