High school student Yako Katsuragi is a gourmand whose father recently died mysteriously. Soon after his death, the demon Neuro Nougami, who feasts on mysteries, suddenly arrives from the Demon World.
Yako's best friend Kanae's friend is the latest victim in a string of murders called the "Zero Case". Her friend had been a part of an internet community called Links.
Kanae invites Yako to go see the popular comedian Taro Manpuku, whose show comes with a bento box. But during his show, several people in the audience collapse and die.
The latest mystery involves a killer who fatally shoots police officers, steals their firearms, and leaves behind a note signed with his self-given nickname, "Cop Killer."
Aya Asia, the singer who has captivated people around the world, makes a surprise visit to Yako's detective agency and asks them to investigate the mysterious deaths of her producer and manager.
Aya's stalker is arrested, but it is determined that he has nothing to do with the deaths of her producer and manager. Yako is getting more and more suspicious of Aya.
Neuro and Yako receive a letter from Sai the Thief, announcing his next crime. Sai says he will steal the sculptor Togo Eshiya's last self-portrait statue.
Yako and her co-workers take advantage of a hot springs trip that she won in a raffle. When they are about to go to sleep at the hotel, they hear shouting.
Lake Kijin is rumored to be home to a dinosaur named Kissie. On their way home from the hot springs, Neuro and the gang come across the scene of a fatal car accident.
There have been several mysterious deaths recently in which the victims have been killed by neuro toxins upon sticking their heads inside the drawer of their red desk.
Neuro and Yako next tackle the investigation of the "Faceless Murder Case". The victim is a female whose face had been completely burned by sulfuric acid.
Yako, Mio, and Godai head to Sharato Village to solve the mystery of the local witch that Haruka had been investigating. Meanwhile, Neuro looks into Laritta Jones' murder.
