Yako Katsuragi, a renowned teenage detective, tackles challenging cases effortlessly with a perfect track record. Behind her agency's success, however, lurks a peculiar secret: her assistant, Neuro Nougami, a demon in human guise. Neuro's insatiable hunger for mysteries propels him to aid Yako covertly in solving crimes, all while masking his true nature. Their partnership unfolds as Neuro seeks the ultimate enigma on Earth, leveraging Yako's quest to unravel her father's mysterious demise. Together, they navigate a delicate balance, with Yako in the limelight as the detective, while Neuro orchestrates solutions from the shadows, fueled by humanity's dark impulses.