Mou gaan dou

The film follows an undercover Hong Kong Police Force officer, Lau Kin-ming (Andy Lau), who infiltrates a triad, and another police officer, Chan Wing-yan (Tony Leung), who is secretly a spy for the same triad. The two men race against time to expose the mole within their midst. After successfully infiltrating the triad, both men are struggling with their double lives, and Chan is eventually betrayed by Lau, leading to a cat-and-mouse game between the two.