Butt Detective the Movie: Shiriarty + The Dream Jumbo Sweet Potato Cake Festival

A baffling series of crimes turns out to be the work of Shiriarty, a villain who seeks to steal a mysterious treasure known as the "O-PARTS". Oshiri Tantei along with his assistant, Brown, enlist the aid of Audrey, an investigator from the international police organization Wanterpol, in an effort to prevent the "O-PARTS" from falling into the wrong hands while Shiriarty strives to plunge the world into darkness.

The owner of Cafe Lucky Cat, located on the first floor of the Oshiri Tantei office, has a back injury and so he cannot do an interview and so Oshiri Tantei takes over for the day. During the interview, a huge order of food arrives by mistake. In order not to let the ingredients go to waste, Oshiri Tantei works everyone in town to make a super-sized sweet potato.