Betrayed and left for dead by treacherous Japanese forces, young samurai Yamada Nagamasa (Seigi Ozeki) is rescued to a remote village in Siam and nursed back to health among the acolytes in the monastery. Working tirelessly to master the art of Muay Boran (Thai boxing), fearless and brutal Yamada is selected to become a royal bodyguard to King Naresuan the Great. His greatest challenge comes on the day he's forced to fight back against the elite Japanese warriors who left him behind.