A 15-year-old runaway is taken in by private detective Shunsuke Utsugi and becomes his assistant. Months later, they are called to investigate the murder of a freshman schoolgirl named Yoko Kojima. Following leads through her high school and the testimony of two friends — Ayumi Tachibana and Hitomi Kawaii — the investigation uncovers a connection to an unsettling school rumor: the tale of a blood-soaked girl who stands behind a student, watching.