Run Papa Run is adapted from a novel by local author Benny Li Shun-yan. Louis Koo plays a gang boss who falls in love with a young lawyer (Rene Liu Ruo-ying). She drags him to the altar after getting knocked up. The triad boss evolves from a gangster to a loving father who does everything to prevent his daughter from knowing what profession he's in.
Yet things turn upside down when rival gangs move in on his turn and his daughter falls for a cop.
Director Sylvia Chang said that the story is interesting because men have two contradictory sides. 'They want to look tough on the outside but actually they are quite soft within. And once they have a child of their own, this soft, childlike side will appear naturally and unintentionally. It's very special.'