The story begins in 1681, 7th year of King Sukjong. Dong Yi lives with her father and brother in a slave village. They are the members of Sword Fraternity, which is the organisation made up of the lowest class people. Then, a high ranking government officer from Southern Faction was assassinated. After that, Dong Yi finds the assassin ID and hand it to the police. But, it belongs to a corrupt policeman who worked for Oh Tae Seok. He is arrested, but gets killed in his prison cell. Dong Yi's father has the information, so Oh Tae Seok's masked man try to kill him but he gets saved by his friend, Cheon Soo. When they get home, Dong Yi is not there. (Source: Viu)