Narumi Detective Agency is where the people of very early modern Japan go to for help with mysterious and supernatural cases. But Narumi is just the face and occasional fist of the operation—the real hero is Kuzunoha Raido, the devil summoner, a stoic young man who seems to seek no credit for his accomplishments. As a powerful devil summoner, Raido can call upon many different demons to assist him in solving cases that deal with other demons causing harm in the human world.

Lately, there has been a surge of cases. A powerful summoner seems to be behind all these incidents. Is the Narumi-Raido combo—plus the latter's talking cat familiar—strong enough to overcome a demon force more powerful than anything they have experienced before?