Fourteen-year-old Seikei accompanies his foster father, Judge Ooka, to help put out a fire in the city of Edo, military capital of 18th-century Japan. They find evidence that someone has set the fire deliberately, and their quest to find out who that person is leads them to Yoshihara—the shadowy city within a city that only comes alive when the sun goes down. Here Japan's famous geishas live and work, entertaining the rich and powerful. The mystery deepens when the Judge discovers that someone has been murdering geishas, and the rumor has spread that the killer is a demon who cannot be stopped. The Judge assigns Seikei to work in one of the teahouses and get to the heart of the mystery—a task that will test Seikei's courage and resourcefulness to the limit.