A low-rank triad member Fat is suddenly told by three charming policewomen that he is an undercover cop but becomes amnesia after an accident. He is given a mission -- to arrest his trial society's boss. Under the cop's command, Fat goes to find out the criminal evidence of the boss. In fact, the boss's wife is Fat's dream lover. He thinks the boss always tortures her, so he wants to rescue her. Actually, boss's wife is planning to get raid of her husband with the help of his follower, and now also with Fat's assistance. At the same time, the boss is trying to cover his real identity by plots... Things become funnier and Fat is falling in love with one of the cops. Is Fat really an undercover? Or is he only a pawn in this game?