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…
Based on the novel by Karel Capek, the prominent Czech writer of the early 20th century who coined the word robot for his play R.U.R., the story revolves around a discovery of Krakatit - a powerful explosive - by Prokop, an experimental scientist who, following an accidental explosion in his lab, slips in and out of delirium. When he realises that, in a delirious period, he has given the formula for making Krakatit to one of his colleagues, he tries to find the man, who does not realize how dangerous a thing Krakatit is. In the process, he nearly gives his discovery away again to foreign interests, a group of anarchists, and even greater forces of darkness...