A lawyer's family is murdered by drug smugglers, and he is beaten and left for dead, but survives although in a coma. When he awakes he only has a partial memory of what happened. In order to find out the real story, he trains with a karate master and becomes a mysterious avenger known as "The Karate Man".

　　几千年前的古老中国，城主为拯救他的子民牺牲自己，化作神奇金牌。直到二十年纪美国考古学家在长沙出土发现双龙金牌，不久即逝世，学世莎是藏起一面金牌并承诺照顾他的两位小孩「比利」和「吉米」二○○七年，全球大地震，美国政府组织亦告瓦解，黑道武器火力超越警方，警方维护白天的和平安宁，黑道帮派则掌控黑夜的利益。十九岁的吉米心思细腻稳重，十七岁的比利体力旺盛心浮气躁，两兄弟平日争斗不休，但对外则行动一致，手足情深，邪恶野心巨贾「古贺」指使猫女「莱倩」偷得半面双龙金牌的下落，查出李氏兄弟。