Agasa takes the Detective Boys on a camping trip when they run into Masumi Sera who eventually joins their camping trip. While Genta, Mitsuhiko, Ayumi, and Haibara collect firewood, they encounter a man burying a female corpse. After being discovered by the killer and being chased by him, they find refuge in a cabin in the woods. While in the cabin, they discover that it was actually the crime scene of the murder. Meanwhile, Agasa, Conan, and Sera start to worry about them because their camping area happens to be out of cell-phone ranges. The Gunma police discover three suspicious men wandering alone in the forest claiming that they were innocent for the murder. While the Gunma police investigate the murder, the Detective Boys realize that they had been locked inside the cabin by the murderer while a fire is starting at the back of the cabin.