Conan suddenly wakes up in the darkness. While walking with the Detective Boys to go shopping, Conan witnessed a figure breaking open a safe inside a building. Conan was attacked by the culprit and imprisoned inside a rectangular box. Meanwhile, Kogoro is hired to find the thief who stole the will of Karabashi Group chairman Karabashi Gotaro. The suspects have been narrowed down to Kozo the eldest son, Mitsuyo the eldest daughter, and Hideo the second son. Conan manages to get in touch with the Detective Boys using his badge, but he soons finds himself cornered in a desperate situation...
