Following an incident where a suspect committed suicide while in her custody, detective Kinoshita Sayaka is forced out of the prefectural police's First Investigative Division. Having also lost her place in her family, she is transferred to a newly formed unit called the Metropolitan Police Special Regional Infiltration Team, a department that has been created specifically for officers who do not fit in elsewhere within the organization.

The first case assigned to the team involves a series of mysterious disappearances of children in a rural village in Tochigi Prefecture, a place where the legend of Yamahito-sama, a mountain spirit said to abduct children, has been passed down for generations. Sayaka and her new colleagues begin an undercover investigation to uncover the truth behind the so-called "Continuous Child Disappearance Incident."

The protagonist, Sayaka Kinoshita, is a capable but intense detective whose relentless pursuit of justice and rigid personality caused friction in both her professional and personal lives, ultimately leading to her divorce. Her new team is a small, mobile unit operating out of a camper van, allowing them to quickly infiltrate and investigate various localities. The team is led by a seemingly laid-back but perceptive superior, Doi, whose calm and包容 (inclusive and accepting) demeanor gradually helps Sayaka begin to soften her hardened worldview.

The narrative primarily follows the investigation into the Tochigi village, where the line between rural folklore and criminal activity blurs. As Sayaka and her team go undercover, they discover that the "kidnappings" are not the work of a monster, but a complex, community-organized system designed to protect children from abusive or neglectful家庭 environments. The village has been secretly sheltering these children, with the Yamahito-sama legend serving as a convenient cover for their disappearances. The children are eventually returned during an autumn festival, at which point the incidents are not reported as crimes, thus preserving the village's secret.

The climax of the first major arc reveals this hidden shelter. Instead of making arrests and dismantling the system, which would return the children to their harmful home situations, the team chooses a different path. They focus on preventing future tragedies by addressing the root cause of the disappearances and finding a way to officially support the village's unofficial, yet effective, method of child protection. This resolution highlights the series' central theme: for this unit, the goal is not simply to solve a crime, but to understand the underlying context in order to prevent future suffering and protect the vulnerable, even if it means operating in a legal gray area.