October 1987, Autumn. In Suganami, Tokyo, lives the Kinoshita family, whose father earns very little from his job as an ordinary salaryman. To cover expenses, he decides to rent out the second floor of their apartment for additional income. One day, an obstinate-looking elderly dog, accompanied by a younger boy-dog, came knocking on their door. The elderly dog introduces himself as Norayama Kuroyoshi and presents his grandson as Norakuro. The former wants to open a detective agency and intends to rent the unit for their office. He will serve as the president of the investigative bureau, while Norakuro-kun will be the director. He also recruits one of the Kinoshita sons, Keita-kun, as an employee, and their advisor will be the girl-next-door, a high school student named Rika Sawaguchi. On the third day since the official opening of the office, the telephone rang, signaling a new case.