Mitsuhiko is missing during the radio taiso day. The Detective Boys ask about his whereabouts from Mitsuhiko's sister and learn he had been going out to an unknown location for the past few Sundays. His sister tells them Mitsuhiko had packed a few Onigiris, and sunscreen. She also tells them Mitsuhiko has been meeting with a girl. The Detective Boys learn from the girl that Mitsuhiko boarded a bus a few hours ago and had an odd smell of lemons. Asking the bus driver, they learn Mitsuhiko boarded the bus and get off at the train station. Asking the ticket administrator, they learn Mitsuhiko headed towards Mount Osutaka. Once at the mountain, Mitsuhiko's Detective Badge is caught on Conan's radar and they follow the location and end up at a forest. There, they find Misao Yamamura who informs them they are chasing after a serial killer who took refuge in the same forest Mitsuhiko is currently in.