Suirin (翠鈴) works as a "Shutō" (司燈), an official responsible for managing the lighting in the inner palace. However, she has a hidden purpose: to find the former fiancé who drove her older sister to her death years ago. Upon learning that the man is now working as a eunuch within the inner palace, Suirin infiltrates the palace by falsifying her age. Frustrated that she cannot find any further clues, her life takes a turn when an incident occurs and she uses the herbal knowledge she cultivated in her apothecary village. This act brings her into deep involvement with a beautiful eunuch named Kōryū (光柳). A mysterious inner palace tale of a young woman pursuing the truth behind her sister's death now begins.