As incidents thought to be the work of a demon known as the kamaitachi occur one after another, Bonzo is murdered in the annex of the inn. Conan notices something odd about the crime scene, and based on the crime scene Heiiji believes the culprit came to the annex through the outdoor bath. After hearing everyone's testimony, Conan and Heiji close in on the truth behind the case and realize who the culprit is from a casual remark...