Keiichi Maebara has just moved to the very small town of Hinamizawa.  He's making friends and generally enjoying his life, until one day, when he learns of a grisly murder that took place in the little village.  His friends won't tell him any of the details, which only adds to his uneasiness.  At the town's yearly festival, he learns that there has been a death on that night every year for four years, and they're all attributed to the Curse of Oyashiro-sama, a punishment for those who supported the dam project that would have put Hinamizawa underwater.  

Another death occurs, and a policeman asks Keiichi for his help investigating what he suspects to be murder.  He informs Keiichi that not only is there a death every year, but someone goes missing.  He warns him not to tell anyone, especially his friend Mion Sonozaki, whose family was heavily involved in the anti-dam protests.  Keiichi only becomes more suspicious, especially when he overhears Mion talking with his friend Rena about how the Oyashiro-sama's Curse would demand one more person.  He confronts Rena about hiding things from him, and she acts like a completely different person, accusing him of lying, as if she knows he's helping the police.  As Keiichi's paranoia mounts, he learns that Rena was listening in on a phone call between him and the police officer.