The series is about a demon, Neuro Nōgami, who feeds on mysteries, and has come to the human world after eating all the mysteries in his. But as a demon, he cannot act overtly. The first thing he does is force a high school girl to become a detective, while Neuro acts as her assistant. While it appeared to be a mystery series early on, the author has described it as "a straight forward entertainment book wearing the skin of a mystery."