O-An, the concubine of the Minamimachi Magistrate, secretly solves difficult cases! The Minamimachi Magistrate, Kamio Izumo no Kami Shigeaki, has his concubine O-An solve difficult cases. O-An's partner is Tamakin, a cat who can speak human language. Despite being insulted by Kamio as a strange drawing, she plays a major role in solving the cases.