Joseon (Korea), 1758. There are few options available to illegitimate daughters in the capital city, but through hard work and study, eighteen-year-old Hyeon has earned a position as a palace nurse. All she wants is to keep her head down, do a good job, and perhaps finally win her estranged father's approval.

But Hyeon is suddenly thrust into the dark and dangerous world of court politics when someone murders four women in a single night, and the prime suspect is Hyeon's closest friend and mentor. Determined to prove her beloved teacher's innocence, Hyeon launches her own secret investigation.

In her hunt for the truth, she encounters Eojin, a young police inspector also searching for the killer. When evidence begins to point to the Crown Prince himself as the murderer, Hyeon and Eojin must work together to search the darkest corners of the palace to uncover the deadly secrets behind the bloodshed.