In the Moon Flower Kingdom, medicinal baths have long been the favored cure for sickness and injury, though traditional remedies there are steeped in superstition and often unreliable. While Prince Keiun is traveling to inspect the regions, his party is attacked by unknown assailants. In the aftermath he sees a lifesaving procedure unlike anything he has encountered, carried out by a young, somewhat eccentric girl named Koyo. Who is she, and who wants the prince dead? Drama and romance meet medicine and court conspiracy in a setting modeled on historical China.