出身于犯罪世家的李志坚（曾志伟 饰）却从小立志做警察。皇天不负苦心人，终于借着警队破例收纳残疾人士的机会，个矮的李志坚如愿加入警队并进入了毒品调查组，在成功完成任务后，志坚再入扫黄组，执行任务期间被流莺恬妞（恬妞 饰）破处并爱上了对方，但恬妞很快消失于茫茫人海。志坚再调重案组，这次的对手是极恶罪犯“无人性”，志坚一举将无人性击毙，引得无人性父亲请出精于乔装的杀手“千面人”（苗侨伟 饰）为儿子报仇，千面人出手连害多名警员，重案组一时风声鹤唳，人人请调，李志坚受命与千面人周旋到底，这位小小小警察的无厘头警员经历该如何收场？

Ever since he was a child, Lee Chi-kin has been determined to become a police officer, despite the fact that he comes from a family of criminals. As an adult, he joins the police force, where he is first placed with the Narcotics Bureau. During a drug raid operation, he catches a drug dealer. He is later transferred, first to the Anti-Porno Bureau where he falls in love with a call girl, then to the Regional Crime Unit where he works under Inspector Chu. During a drug raid operation, Lee kills drug lord Ng Cheung. Ng's father hires a killer, Thousand Faces Man to take revenge on Lee. After several confrontations, Lee finally brings Thousand Faces Man to justice. The corrupt director of a mental hospital places Lee in the mental hospital for a year, during which time he develops mental disorders. After being discharged from the hospital, he becomes a restaurant waiter.