Kogoro receives a request from a letter by Mika Tatezato to investigate the murder that occurred at an inn eleven years ago. On the way, they pick up a teacher named Rokurou Tokobi who requests for them to stop by a grave site before heading to the inn. Tokobi explains that Tatsuhiko Numayama, a student of his, drowned in the river by the inn which is owned by Tatsuhiko's father, Banzou Numayama.