Kim Seong Yeol is a scholar and a long time friend of the crown prince Jeong Hyeon. Before his planned marriage with the girl he loves, Seong Yeol learns the horrific truth about the royalty of Joseon and the existence of Gwi, a powerful vampire who demands submission from the king himself. When the plan to destroy Gwi fails, Seong Yeol loses everything he holds dear, including his love and humanity.
Jo Yang Sun (Lee Yoo Bi) is the daughter of a nobleman who loses everything after he is wrongfully charged with a crime. In order to help support her fallen family, Yang Sun dresses as a man in order to sell books at the market. One night, she meets a handsome scholar, Kim Sung Yeol (Lee Joon Gi), who also happens to be a vampire. Can Yang Sun help Sung Yeol stop a more sinister vampire within the palace from overthrowing the throne?