Set in an alternate version of the Joseon dynasty, a cross-dressing bookseller struggling to make ends meet named Jo Yang Seon (Lee Yu Bi) meets the handsome and mysterious scholar Kim Sung Yeol (Lee Joon Gi). Unfortunately for Yang Seon, Sung Yeol is a vampire, and he is haunted by the loss of his first love Lee Myung Hee over a century ago. Seeking revenge for her death, things are further complicated when he meets Myung Hee's present-day doppelganger Choi Hye Ryung (Kim So Eun), an aloof nobleman's daughter. Meanwhile, the evil vampire Gwi (Lee Soo Hyuk) responsible for Myung Hee's death resides in the royal palace and uses his powers and political machinations to prevent the Crown Prince (Shim Chang Min) from ascending the throne.
- Bookworm: Yang Seon.
- Combat Parkour: Sung Yeol is fond of this.
- Daywalking Vampire: Sung Yeol can walk around during the day just fine, only experiencing discomfort/burning when sunlight touches his skin directly.
- Death by Origin Story: Myun Hee.
- Died in Your Arms Tonight: Myun Hee again.
- Gorgeous Period Dress: It's a drama full of Joseon nobles. Gwi's embroidered robe particularly springs to mind.
- Heroic Sacrifice: Myun Hee running into Gwi's knife so that Sung Yeol can feed on her and survive.
- It's All My Fault: Sung Yeol murmurs this while unconcious and reliving Myung Hee's death.
- Masquerading As the Unseen: Lee Yoon, the Crown prince pretends to be the Lustful Scholar, the Pen Name of the Crown Prince a century prior. This leads to much confusion for Sung Yeol.
- Mistaken for Gay: Some gisaengs assume Sung Yeol is gay because he has no interest in them, and warn Yang Seon that 'he' should watch out, since a feminine guy like him is probably Sung Yeol's type.
- Plucky Girl: Yang Seon seems to be shaping up to this. Despite being chased by loan sharks, nearly eaten by the undead, and under the pressure of supporting her entire family, she's still determined to help Sung Yeol, despite the dangers. And she finds time to dance in the rain.
- Puppet King: It's implied a number of the current dynasty's Kings have been these thanks to Gwi.
- Raised as the Opposite Gender: A strange case with Yang Seon, who was raised, dressed and acted like a boy after an accident when she was little caused a monk to advise the family to do so (the show so far hasn't really expanded on this). However, she still thinks of herself as a woman, as do her relatives.
- Royals Who Actually Do Something: In contrast to the Kings, all of the Crown Princes mentioned in the show have been actively trying to stop Gwi and free Joseon from his influence. it doesn't go well for the first two, unfortunately.
- Thinking Out Loud: Yang Seon does this quite often.