Genta assists the cook Shigeru Unagizuka from "Ginpachi Unagi Shop" with eel deliveries for the "Midsummer Ox Day" when he injures his foot. During the delivery, Genta meets Conan and the Detective Boys. Later, Unagizuka is found with an eel preparation needle (perforator) in his chest and is severely injured, being taken to the hospital. Genta, furious about the attack on his mentor, decides to catch the perpetrator. The investigation reveals that the crime took place between 3:30 PM and 4:30 PM. Suspects are:

- Yuya Kurashima (soy sauce manufacturer), who discovered Unagizuka at 4:30 PM;
- Hiroyuki Okamoto (event manager), who argued with Unagizuka at 3:30 PM;
- Rio Matsui (last customer), who was in the shop between 3:45 PM and 4:15 PM.

While eating an eel bowl at Matsui's, Genta notices an unusual taste. His expertise tells him: The eel was prepared in the Kansai style (opened from the belly) instead of the usual Kanto style (opened from the back). Additionally, a grilling fan – a tool for roasting over charcoal – is missing from the shop. Conan deduces that the culprit pretended to be a cook during the crime when Matsui picked up her food. Okamoto, a former cook from Kansai, is exposed when Genta finds the stolen fan in his office. After a brief chase, Okamoto is arrested.