Set in an alternate Joseon dynasty, Jo Yang Sun (Lee Yoo 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). Sung Yeol is a vampire, and he continues to be haunted by the long-ago death of his first love Lee Myung Hee (Kim So Eun) once 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 Yun (Shim Chang Min) from ascending the throne.