A young apothecary named Maomao is kidnapped and sold into servitude, finding herself trapped within the sprawling complex of the inner palace, the imperial harem reserved solely for the emperor. Determined to blend in and serve her term quietly, she tries to hide her extensive knowledge of herbs and medicine. However, her innate curiosity gets the better of her when rumors of a curse causing the emperor's infant children to die begin to circulate. Using her wits, Maomao investigates the mysterious deaths and secretly intervenes to save a life.

Her actions do not go unnoticed. The beautiful and enigmatic eunuch Jinshi, who serves as the palace overseer, sees through her facade. Instead of punishing her for meddling, he orchestrates her promotion to lady-in-waiting and food taster for one of the emperor's favorite concubines, the kind and perceptive Consort Gyokuyo. This role is perfectly suited to Maomao’s skills, as her knowledge of medicine, herbs, and poisons makes her an ideal taster, though she would much prefer a quiet life tending to her remedies.

The inner palace is a world unto itself, a city of thousands of women, including high-ranking consorts, ladies-in-waiting, and lowly maidservants, all managed by eunuchs. It is a place of intense political maneuvering, gossip, simmering rivalries, and hidden dangers, where a single misstep can be fatal. As Maomao is drawn into this world, she begins a series of investigations, using her sharp observational skills and pharmaceutical expertise to solve various mysteries, from attempted poisonings and strange ailments to suspicious deaths.

The narrative unfolds through several notable arcs. Early on, Maomao investigates the deaths of the emperor's children, an incident that first brings her to Jinshi's attention. She later uncovers the truth behind a series of colored fires and an allergy involving honey that implicates the household of Consort Ah-Duo, uncovering a complex web of past relationships and secrets connected to her own adoptive father, a former palace doctor. Eventually, Maomao is forced to leave the inner palace and begins working in the outer palace, where government officials and military officers conduct the nation's business. There, her insatiable curiosity is piqued by a forbidden wing occupied by soldiers, leading to further mysteries. Later volumes see her investigating everything from cosmetic ingredients and an outbreak of syphilis to the perplexing rules of an ancient shrine and the dark history of the Empress Dowager. Throughout it all, Maomao’s reluctant partnership with the manipulative and ever-annoying Jinshi deepens, even as she remains most passionate about the science of poisons and the simple art of brewing medicine.