Old Mr. Lo has three sons and the youngest one Lo Kung is his favorite. However, Kung does nothing but fool around all day long. Old Mr. Lo is very annoyed about this. The relationship between father and son is thus affected. So on Kung's birthday, his two brothers decide to play a joke on him. They trick him into believing he has won the lottery. Kung is so happy that he spends a tremendous amount of money. When he realizes he is in huge debt, he pretends to go insane and the whole family believes him.

霍启发（任贤齐饰）事业有成，收入不菲，却为女朋友一事而苦恼。他女友Rachel（徐子珊饰）甚为西化，着装开放暴露，正是见家长的大忌。父母催婚，为了让他们接受Rachel ，霍启发决定征选合约情人，带回老家。
刘枣（范冰冰饰）是待业大学生，家境贫寒，应征成功令她开始了合约情人的身份。霍启发带她来到佛山老家，让她做尽令老人家失望之事。但刘枣和霍家关系竟越来越好，事情竟然往料想不到的方向发展。霍启发、Rachel和刘枣三人之间如何纠结？刘枣这个情人到底有多长的合约？