Time is A.D. 927, when Georan invaders have conquered the ancient Korean capital of Balhae and set up a new country, Dongran-guk. The leaders of Balhae desperately need a royal figure to reunite their nation. They find a prince, the previously exiled Dae Jeong-hyeon, who's hiding out under the name So-sam. The leaders dispatch a peerless swordswoman, Yeon So-ha, to protect So-sam before Georan's Killer Blade Army, commanded by Gun-hwa-pyeong, find him first. Initially, he sends his deputy, Mae-yeong-ok, to handle the situation: She wants to become the greatest swordswoman of the age and knows she must first kill Yeon.