Mysterious Heroes centers around Lau Tien, master of the deadly 13-Sword Style. Thrown into prison by a group of jealous enemies, the 13-Sword Style is rarely spoken of, let alone seen, until 20 years later, when a second swordsman going by the name of Lau Tien proves to be the world's second 13-Sword expert. Action-packed martial arts chaos ensues when the enemies of the original Lau Tien vow to destroy his successor.

The plot deals with a search for a valuable pearl, dubbed the Buddha's Relic, which is sold to an unwitting Japanese emissary by a corrupt Ching Dynasty prince who seeks to steal it back for his own purposes.