The Detective Boys are stranded on a mountain when Agasa's car breaks down. Seeking shelter from the rain they come across a villa where piano music was heard and enter the house when their calls are unanswered. Inside, they explore and discover a diary on the table confessing to a plan of a kidnapping and murdering a boy; a blackout then occurs due to the storm. They find a small coffin planned for the murder and realize its empty and the possibility the boy is still be alive. At that moment, piano music is heard again. Conan assures them it will be safe to search the house as the culprit is playing the piano. Ayumi wanders off on her own and finds a photo of a family and a room with water leaking out of it.