Two melancholic Hong Kong policemen fall in love: one with a mysterious underworld figure, the other with a beautiful and ethereal server at a late-night restaurant.

Chan Wing Yan, a young police officer, has been sent undercover as a mole in the local mafia. Lau Kin Ming, a young mafia member, infiltrates the police force. Years later, their older counterparts, Chen Wing Yan and Inspector Lau Kin Ming, respectively, race against time to expose the mole within their midst.

Chingmy Yau is spunky girl-next-door Tung-Tung, who's hot for rich guy Wing (Tony Leung Chiu-Wai), but she can’t say two words to him thanks to one of those afflictions that occurs only in movies. It seems she has this annoying problem of hyperventilating whenever a guy she likes looks at her.