In a fictional country based on ancient China , Maomao, a young girl who works as an apothecary in the red-light district, is kidnapped and sold to the Imperial Palace as a servant. However, she still retains her curious and eccentric personality and plans to work there until her years of servitude are over, without drawing the attention of anyone. One day, after hearing the rumors that the emperor's children are critically ill, she begins to investigate the cause, using her experience as a pharmacist, and successfully solves the mystery of their illness. Even though she intends to remain anonymous, her actions eventually catch the attention of an influential eunuch, and soon finds herself solving various mysteries in the royal court.