宋末蒙古蒙哥(gē )大汗(hàn )南下侵宋,途中遇到飞(fēi )天炮阻击身(shēn )受重(chóng )伤。后法王虽偷得飞天(tiān )炮,然蒙哥伤(shāng )势加(jiā )重,只得撤兵。返程中被(bèi )忽必烈偷袭(xí ),逃入(rù )雪山。蒙哥感到命不久(jiǔ )已,写下血书(shū ),传位尚年幼王子海都后自(zì )尽。大雪山中(zhōng )人马走散,飞天炮和血书失(shī )踪,海(hǎi )都逃出雪山后遇到受伤的法王,原(yuán )来他(tā )受到中原三大高手的袭击,他们一(yī )起返(fǎn )回雪山找寻其它队伍(wǔ )但是雪山迷(mí )宫使(shǐ )他们放弃。与此同时三(sān )大高手也感(gǎn )无力(lì )进入雪山,将进雪山迷(mí )城的地图分(fèn )成三(sān )份交各人保存。法王带(dài )着海都勉强(qiáng )到达师弟银枪法王处,将海(hǎi )都托付给师弟后毒发身亡。海都从此身(shēn )负夺(duó )回帝位的重任。