A young man wants to be a Hong Kong police officer but is too short to qualify. However, he doesn't let that stop him: he goes around impersonating an officer, investigating crimes and busting criminals. One day, he interrupts a bank robbery (by three men in drag), gets shot in the process and dies. When the case is assigned to a female investigator, he returns as a ghost to lend a hand at solving the robbery.

五代服役于警界，成男子汉家族，竟出吕方没法传誉之后代。为家族声誉，吕方成为“神秘CID”冒充警察捕罪犯，终于上得山多终遇虎，在势案中被女劫匪打死。大丈夫吕方灵魂不息，成为鬼魂誓要为己报仇，谁知负责此案的警司竟是霸王花，吕方不信女性办事能力大闹警局，与警员冯淬帆、孟海结为好友，联手查案，展开一场人鬼联手，终将匪伏法，含笑轮回而去。