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.

Sung-yeol continues to be haunted by the long-ago death of his first love, Lee Myung-hee (Kim So-eun), who sacrificed herself for him 120 years ago.

Sung-yeol decides to pay Yang-sun a high price if she is able to find the memorandum of his best friend, the late Crown Prince Jonghyun, which contains the secret to killing Gwi (Lee Soo-hyuk) and avenge the death of his family and lover.

On a trip to find the old book seller from Yuan with Yang-sun, Sung-yeol meets Choi Hye-ryung, Myung-hee's present-day doppelgänger who is an aloof nobleman's daughter.

However, due to her loyalty and gentle treatment towards Gwi, he has unconsciously fallen in love with Hye-ryung and secretly plans to change her into a vampire, even though he already has 100% control of the royal court.

Jo Seung, Yang-sun's adopted father, is the secret keeper of the Crown Prince Jonghyun's memorandum.

Her biological mother had raised her as a boy in order to protect her because she knows that her daughter needs to be sacrificed as a weapon to kill Gwi.