In the intense psychological crime thriller, Infernal Affairs, a cop (Tony Leung) goes undercover as a gangster while, simultaneously, a gangster (Andy Lau) infiltrates the police force, pretending to be a cop. These two sleeper agents live underground for a decade before a series of mistakes clues in all the wrong people as to what's going on and each mole is ordered to root out the double agent -- which in both cases happens to be themselves.
Torn between conflicting father figures -- an avuncular, paranoid gang boss (Eric Tsang) and a morally compromised police superintendent (Anthony Wong) -- the two moles slowly feel the net tighten like an icy hand around their necks.
Juggling identities, always one mistake away from a bullet in the head, and seduced by the attractions of their cover identities, both men slowly unravel, battering themselves bloody against the bars of their own personal hells, while their souls ice over. One of the biggest hits of 2002, Infernal Affairs, has scored at every box office in Asia, from Hong Kong to Japan. It's a big-budget throwback to the intensely acted psychological crime dramas that ruled Hollywood in the 1970's.