本片用惊悚手法,折射现今追求以瘦为美、过分瘦身的风气。 瘦身比赛开始前夕,女明星Ivy神秘遇害,这桩案件的调查者是警员黄秋德(黄秋生 饰),他有一个极有侦探头脑的老婆玲(邓萃雯 饰)。黄秋德在调查过程中,预料到其他出席比赛的人亦有被害危险,其中包括Queenie。 随着离奇遇害者越来越多,黄秋德的调查也陷入了僵局。束手无策中,玲提出了一个别出心裁的破案思路,让案件有了柳暗花明的转折。嫌疑焦点落在了Queenie的助手Cherrie(应采儿 饰)上,还没有来得及搜集足够线索,玲已不幸成为下一个猎物。原来,Cherrie发明了一种疯狂的杀人方法,让所有人在瘦身中残忍死去!玲的生命岌岌可危,她必须逃出这个致命游戏。Sergeant Tak (Anthony Wong) must track down a serial killer whose victims are starved, mutilated, and killed, and weighing exactly 70 pounds. The victims have an unexplainable link to a TV show which runs a beauty contest called "Slim Queen", where they appear as contestants. The plot thickens as Sergeant Tak and his wife, Ling, an ex-detective herself, race to find the murderer before more contestants end up dead.