Star Chow (Stephen Chow) is about to be kicked out of the Royal Hong Kong Police's elite Special Duties Unit (SDU). But a senior officer decides to give him one last chance: Star must go undercover as a student at the Edinburgh High School in Hong Kong to recover the senior officer's missing revolver. The undercover operation is made complicated when Star is partnered with Tat - an aging, incompetent police detective (Ng Man-Tat). However, Star still manages to fall in love with Ms Ho (Cheung Man), the school's guidance counselor, as well as disrupting a gang involved in arms-dealing.