While hiking, Kogoro, Conan, and Ran hear the moaning voice of the tengu, a mythical dog-like creature. After staying the night at a guest house at the bottom of the mountain, they decide to visit the tengu's cave, one of the town's historic sites. Inside the cave, Conan discovers a body wearing a tengu mask hanging from the shrine. The body belongs to Mayor Shoji Mayama. Kogoro determines the death is a suicide based on the absence of anyone else in the cave, but Conan feels there's something off about the body and crime scene.