Conan and the Detective Boys, accompanied by their teacher Ms. Koyabashi, are on a school field trip to a food factory. Disinterested, Conan listens to the soccer game on his MP3 player which is confiscated by Koyabashi. They are given a tour of the facility by employees Kashiwa and Minamoto. Minamoto abruptly leaves, leaving Kashiwa to handle the tour on her own. An hour after the tour, and as promised for being good students, Kashiwa gives the kids ice cream. She opens the door and discovers Minamoto on the floor, face up, frozen to death. An investigation is launched and everyone assumes Minamoto slipped and was stuck to the floor, until Conan discovers a pack of broken rice crackers in the victim’s pocket. Conan believes that someone knocked Minamoto unconscious, causing him to fall facing the front thereby breaking the rice crackers, then turned him on his back. It is now possible that Minamoto had been murdered.
Minamoto’s death was the result of a heinous murder and the culprit is his coworker, Kashiwa. She knocked him unconscious with a small tank containing liquid nitrogen, a cryogenic liquified gas capable of freezing human flesh almost instantly upon contact.
Minamoto was a well-known slacker at work and often left Kashiwa to handle his duties, as such at the beginning of the tour. Due to his negligence on the job, Kashiwa set him up by telling that the best hiding place was the freezing unit.