警方卧底因为演技太差，被黑帮老大识破并杀害。处长（许鞍华 饰）决定寻找警界里最有表演欲的警员到演艺学院学习演技。连sir（许绍雄 饰）找到了极具表演欲的陈文龙（詹瑞文 饰），委以重任。文龙十分热爱演戏，他有一个恋爱7年的女友Judy（叶璇 饰），但两人貌合神离。跟文龙一样是插班生的单丹（蔡卓妍 饰）是一个三级片女星，她的身份被很多人歧视，但仍然坚持学好演技。同时文龙也因为他夸张的演技受到侧目。 单丹与文龙二人可谓同病相怜，也因此成为了好友。满以为自己的演技已有所提高，文龙接受了上司安排的行动，但终告失败了。他也被上司勒令退学了，之后他得到了高人（黄秋生 饰）的指点，真正了解了演戏的真谛。Man Long Chan, a constable whose antics and showmanship win him best performance awards at the Force's annual parties, is handpicked by the Deputy Police Commissioner to enroll incognito into a Performance Arts Academy as an experiment in upgrading police acting abilities. Man Long is thrilled that his lifelong acting dreams are finally going to be realized, but quickly finds out that his plain looks and exaggerated performance skills are no match to his younger and better looking classmates. His only good friend in class is a fellow mid-term new student Dani, whose claim to fame is starring in a string of skin flicks, but is an aspiring actress with a heart of gold. Man Long's confidence plunges into a downward spiral when he fails in a police operation and nearly loses his life. Then a favor he extends to Dani turns into an outright expulsion from the academy. In his darkest moments he meets a stage janitor whose priceless insights into acting teaches Man Long that the Bard was right in saying that all the world is a stage, and all the men and women are simply actors. We slip in and out of different roles in our everyday lives and the best acting can be cultivated when you pay attention to what you do every second of everyday. In the end, Man Long returns to the Force with a renewed understanding of what it takes to be a good actor. He transplants his new-found knowledge into the future generation of undercovers whose lives will be spared because of Man Long's acting classes.
