Set in the Joseon era, the drama follows bookseller Yang-sun (Lee Yu-bi) who is disguised as a man to sell books and make ends meet. She comes to the attention of the mysterious scholar Kim Sung-yeol (Lee Joon-gi) when he discovers she is selling rare books. Thinking she may be able to find a memorandum that was owned by his best friend the late Crown Prince Jonghyun (Lee Hyun-woo), he asks her for help.