Set in an alternate Joseon dynasty, Jo Yang-sun (Lee Yu Bi) is the daughter of a nobleman whose family loses everything when her father is framed for treason. To make ends meet, Yang-sun begins cross-dressing as a male bookseller, and meets the handsome and mysterious scholar Kim Sung-yeol (Lee Joon Ki), who works at the Hongmungwan. Sung-yeol is a vampire, and he continues to be haunted by the long-ago death of his first love Lee Myung-hee, especially when he meets Myung-hee's present-day doppelgänger Choi Hye-ryung (Kim So Eun), an aloof nobleman's daughter. Meanwhile, the evil vampire Gwi (Lee Soo Hyuk) resides in the royal palace and uses his powers and political machinations to prevent the Crown Prince Lee Yoon (Shim Chang-Min) from ascending the throne.
