Keita Kinoshita is a 10-year-old boy living with his parents, Kinoshita Keisuke and Kinoshita Keiko, in Tokyo's Suganami ward. To supplement the family income, his father rented out their apartment's second floor. The tenants are an elderly dog named Norayama Kuroyoshi and his grandson, Norakuro, who established the "Norakuro Detective Agency" there.

Keita became an employee of the agency, working directly under director Norakuro. Their advisor is Rika Sawaguchi, a high school student residing next door. Balancing his elementary school life with his detective duties, Keita helped the agency open for business.

The agency's cases, often involving unusual or mysterious client requests investigated directly from Keita's home, frequently disrupted the Kinoshita family's previously peaceful routine. Keita's classmate, Ranbou, is part of his social circle.