阿东（张智霖 饰）、阿郎（葛民辉 饰）和布拉德（许志安 饰）是同居一室的室友兼好友。阿东和女友（汤宝如 饰）相恋多年，彼此之间感情十分稳定。然而，这段波澜不惊的感情却令阿东感到乏味和疲惫。
某日，阿东偶然之中遇见了久别的漂亮表妹，热情活泼的表妹很快就吸引了阿东的注意，在表妹身上，阿东寻得了久违的激情和重获青春的感情。然而，女友对自己的依恋让阿东无法和她说出实情，夹在两个女人之间，阿东苦苦无法做出选择。布拉德向来喜欢流连于莺莺燕燕之中，风流快活，哪知道一位神秘女子的出现，竟然让一向洒脱的布拉德陷入了苦恋之中。

The "Hu-Du-Men" (loosely translated as "stage door") is an imaginary line separating the stage from reality, and a line that must be crossed each and every night by Sum (Josephine Siao), the aging star of a Cantonese Opera troupe. Nearing the twilight of a storied career, Sum must face a variety of challenging new obstacles, including the possible emigration of her family come 1997, the appearance of a promising young actress (Anita Yuen), the hiring of a Western-schooled stage director (David Wu), the surprising revelation of her daughter's sexuality, and finally the reappearance of a shocking secret from her past. Through it all, Sum must retain her professionalism and dignity, as the "Hu-Du-Men" between the stage and her life begins to blur. Emotional, intimate direction and Raymond To's intelligent, relevant screenplay make Hu-Du-Men worthwhile cinema, but it's Josephine Siao's brilliant, emotionally dynamic performance that sets this film above the rest.

From an unhappy childhood experience, Law Ka Sing decisively hides his homosexual identity. Sing's partner of 8 years, young boyfriend Sunny is just the opposite, he has never minded publicly revealing his identity.