In 19th century Asia, Yang (Jang Dong-gun) is a warrior and member of the Sad Flutes clan, the cruelest assassins in the east. His personal goal to become the greatest swordsman in the entire world is accomplished when he kills the former greatest swordsman in the entire world and leader of the enemy clan. Both clans swore to fight until every single member of the opposing clan was dead. Yang has killed every member, except a baby girl he comes upon, spares and decides to watch over. This act makes Yang a sworn enemy of his own clan, and forces him to flee his homeland.