Seventeen-year-old girl detective Mikage Misasagi goes around clad like a shrine maiden in white kimono and red hakama trousers, claiming to be able to "see through the truth" with the green crystal prosthetic she wears in place of her left eye. Having inherited the name and look of her mother, a brilliant sleuth who died when her daughter was a year old, Mikage is now learning her trade under the tutelage of her father, Yamashina, a former police detective. While staying with her father in the remote mountain village of Sugaru, Mikage takes on her first case, a killing within the village's most distinguished household. With a history dating back more than a thousand years, the Kotosaki family has passed the revered ritual position of "Sugaru-sama" down through its women over the generations. The murder victim is the eldest of the current Sugaru-sama's 15-year-old triplet daughters, Haruna, who was beheaded in the midst of being groomed to succeed her sickly mother. Despite strict vigilance, Haruna's sisters Natsuna and Akina also turn up as decapitated bodies, following which the killer strikes down Mikage's father. Mikage meanwhile conducts her investigation with the help of Taneda, a university student who came to the village intending to commit suicide. After a brief setback she points the finger at Sugaru-sama, whose confession puts an end to the mystery—or so it seems. Eighteen years later, in 2003, the eldest daughter of the new Sugaru-sama is again beheaded, prompting a third Mikage (the daughter of the second) to reopen the case. Who is the real killer? The answer, revealed in the final pages, is guaranteed to astonish.