With Mion's name clearly printed among the names of those killed in Hinamizawa twenty years ago, suspicion for the murder falls on her.
But Mion isn't the only one whose story doesn't quite add up.
How did the killer know Otobe's was the only phone with a signal?
How could Otobe's friends have simply 'disappeared'?
Is it really the work of demons, or is there a murderer among them?