五千年来，血魔反复再生作崇，附于有权势者身上，置人民于水深火热中，抗日年间，镇魔师梁初三与师兄合力将血魔镇服，可师兄身死，留下天赋异禀的孤雏林刚（林正英 饰）予初三抚养。一晃多年，十年动乱中，初三之子梁国栋（梁家辉 饰）检举父亲，投身“革命”。两年后，劳改归来的林刚与经历现实磨砺、丧失革命锐气的梁国栋重逢，二人在工地惊见血魔封印破坏，而当年的“臭老九”、今日的革委会领导雷复鸣被血魔附身，预备用手中权势掀起血海……另一方面，对血魔尚不知情的林刚、国栋二人渐渐明白了他们父辈当年的作为，同时对雷复鸣之女雷珊（王祖贤 饰）暗生情愫，但他们和血魔的血战，不可避免…

A two-timing bigamist finds himself concocting scheme after scheme with his best friend, Chi Hung, to prevent either of his wives from discovering his bigamy. The unwanted intervention of a police officer as well as a series of unfortunate events lead to the wives discovery of the whole plot. They team up with Chi Hung's exasperated fiancée, Ka Lai, to exact revenge upon the two men.