Star Chow (Stephen Chow) is a member of the elite Special Duties Unit of the Royal Hong Kong Police Force (SDU). Star jokes with his senior officer, Inspector Yip (Deanie Ip), that he wants to be sent to the traffic section at a meeting. Star is quickly demoted to Constable, and he is sent to traffic duty on Hong Kong's streets. Star resigns from the police force hurriedly after being made the scapegoat for a botched high school terrorist investigation. He enrolls in high school in order to conduct his own private investigation. When Star sees that the stupid, inept CID detective Tat (Ng Man Tat) is also undercover at the high school, he realizes that the investigation will be difficult.