Andy is a writer for newspaper classifieds who has been bouncing from relationship-to-relationship since sixth grade. Throughout the film, he loses custody of his dog when his girlfriend, Cheryl, breaks up with him for another man. Andy then meets Lorna, a children's TV show host, but she is too obsessed with her own dog to commit to a relationship with Andy. She's also still smiting because her boyfriend Trevor, left her for Andy's ex, Cheryl. Andy also has a fling with another woman, Keiran. Meanwhile, Cheryl takes Andy's dog to a psychiatrist, who tells her that her promiscuity is traumatizing the dog.
美发师纪阿开（张学友）、服装设计师大眼龙（莫少聪）和风水师赖布丁（周星驰）三个死党合伙开了一家新潮美发店，不料开业当天就与隔壁理发店老板发生争执，幸得店老板女儿亚英（张敏）及时出手风波平息，过程中，三人皆被亚英魅力吸引，为赢其芳心，开始频频登其家门献殷勤。 某次晚餐聚会后，三人烂醉与亚英误睡一室，导致亚英怀孕，为与亚英一起生活，三人争先恐后将准父亲一职往自己身上揽，又因三人血型相同，医院也无法验出谁在冒名，亚英父母决定先考察三人表现，为争当最佳女婿，三人使尽浑身解数展开激烈角逐。
