Mai meets Naru while exchanging ghost stories with her friends, and learns her school principal has hired him to investigate an allegedly haunted school building. Mai later causes the injury of Naru's assistant and is forced to stand in as a temporary replacement. The principal also brings in several exorcists and mediums, and more help arrives in the form of a classmate of Mai's, who claims to have the ability to sense spirits.

Each member of the team proposes a different theory as to what is responsible for the odd occurrences. After collecting data overnight, Naru begins to doubt the presence of any spirits and instead theorises that land subsidence is the cause of all the ghostly activity. Mai's classmate, Kuroda, fiercely insists that a poltergeist is at work, and evidence appearing to support her idea soon arises.

After disappearing for a night, Naru conducts an experiment involving all those associated with the case. He implants a hypnotic suggestion in their minds regarding a chair in a sealed room moving overnight. His experiment proving successful, Naru reveals his explanation for the latest developments, correctly accusing one of the group of mimicking a poltergeist's acts. After the conclusion of the case, Naru offers Mai a part-time job at the SPR, which she accepts.

The SPR team, joined by the exorcists and mediums from the previous case, are requested at a house where poltergeist-like activity has been taking place. Soon after their arrival, the ghostly occurrences escalate, leading Bou-san to conclude the house is haunted by something more than a mere poltergeist. A young girl in the family, Ayami, exhibits strange behavior, claiming her doll Minnie has been speaking to her. The SPR team observe Minnie closely, with disturbing results.

Ayami reveals Minnie has been exerting a strict control over her, punishing her whenever she breaks a promise to Minnie. The team believes the doll is being used as a vessel by a spirit. After Ayami is involved in a near-fatal accident, Naru discovers previous residents of the house have been plagued with frightening incidents, all resulting in the death of young children.