Kogoro, Conan, and Ran are visiting Nagano Prefecture when they run into Inspector Yamato and his associates of the Nagano Prefectural Police. Conan and his friends visit the Kansuke Shrine ruins and Yamamoto Kansuke's grave. While visiting the Chikumagawa River, their final destination, Inspector Shigeru Takeda's severed head is found in the river. On the body's forehead is a mark resembling a woodpecker's footprint. Allegedly, a mysterious group known as the Woodpecker Society exists in the Nagano Prefectural Police. Yamato and his associates search for someone who may have borne a grudge against Takeda when two cases involving Takeda resurface.
