Mini Mo（郑秀文饰）遭受失恋的打击后，饮食失去控制后体重升至260磅，窈窕身材不再。她与初恋情人黑川约定在十年后的日本相见，但旧貌不再的她深感自卑。偶然相识了跟她同样体型极胖的肥佬（刘德华饰），肥佬非常同情她，决定要帮她重塑魔鬼身材。肥佬以地狱式减肥方法锻炼Mini，为了让她减肥成功，得到更多的金钱让她上专业美容院减肥，肥佬不惜在街头被拳击换取酬劳。令Mini感动不已。 Mini恢复原貌前去赴约，黑川向她提出求婚，可是她心中仍念念不忘为她默默付出的肥佬，盼望跟他重逢的一天。Sammi Cheng plays Mimi Mo, a young exchange student to Japan who met and fell in love with a budding pianist, Kurokawa, played by Rikiya Kurokawa. Kurokawa eventually leaves to study music in the USA and returns to Japan as a famous musician. Meanwhile, Mimi has dealt with her depression by eating and weights over 300lbs and Kurokawa doesn't recognize her. Mimi eventually meets Fatty (Andy Lau) who helps her lose the weight so she can fulfill her promise of meeting Kurokawa made 10 years earlier. But then they fall in love.....
