在刑事部队内的英雄阿杰 (张学友 饰) 与父亲肥波 (吴孟达 饰) 之间并不和睦。肥波当年因为对重案组长洪坤（秦沛 饰）的仇恨，被迫逃亡生活。一个不幸的日子里，他在与流氓打斗时错杀了自己大儿子。阿杰因此永远难以原谅父亲。肥波已经退休，在夜总会上班，有个做舞女的女友阿红 (吴家丽 饰)。
阿杰 heroically rescued Heidi (郑秀文 饰) from kidnappers, sparking a warm friendship between the two. However, tragedy strikes as it is revealed that Heidi is none other than tyrannical gang leader Hongkun's daughter. Unyielding and ruthless, Hongkun vows to tear apart Heidi and Ahjie, even going so far as to hire assassins to pursue Ahjie.
Desperate to protect his son, Beipo tragically sacrifices himself in a fire. Determined to seek revenge against Hongkun, Ahjie swears vengeance. However, Heidi intervenes once again, this time trying to prevent Ahjie from pursuing their dangerous path...
