The time is A.D. 927, when Georan invaders 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, finds 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.