While hiking, Kogoro, Conan, and Ran hear the moaning voice of the Tengu. After staying the night at a guest house at the bottom of the mountain, the next morning 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 Tengu's shrine. The body belongs to mayor Mayama. Mayama was being blackmailed by someone over the undocumented contributions he received during the election. 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...