When 1930s Tokyo is threatened by a master thief who can disguise himself to look like anyone, and laughs at the law, the people of the city have nowhere else to turn but Japan's greatest detective, Akechi Kogoro. Unfortunately for Tokyo, however, Akechi Kogoro is off on overseas business, so it becomes the job of his 12-year old assistant, Kobayashi Yoshio, to track down the thief and desperately keep him at bay until his mentor returns.