In the autumn of October 1987, the Kinoshita family resides in Suganami, Tokyo, where the father struggles with the meager income of his salaryman position. To help cover household expenses, he opts to rent out the apartment's second floor. The arrangement changes when an elderly dog with a stubborn demeanor and a younger canine companion arrive seeking space. The elder introduces himself as Norayama Kuroyoshi and presents his grandson as Norakuro. They plan to establish a detective agency in the unit, with Norayama serving as the agency president and Norakuro taking on the role of director. They also enlist Keita-kun, one of the Kinoshita sons, as staff, while Rika Sawaguchi, a high school student from the neighboring residence, agrees to act as their advisor. Just three days after the office officially opens, the phone rings, marking the beginning of their first case.