The secret is out! The mystery of the suspicious murders has been revealed: The deaths are the result of a parasite spread throughout Hinamizawa by Oyashiro-sama fanatics. They intend to keep control of the village by wiping any nonbelievers or defiers of "Oyashiro-sama's will." The parasites cause people to get the sensation of having maggots under their skin, particularly their necks, which would explain one of the repeated deaths throughout the different and separate arcs of the series: clawing out one's own throat. Having read Nurse Takano's scrapbook, Rena believes it completely and is convinced that the fanatics are targeting her for death, seeing as she once left the village and felt compelled to return --- another side effect of the parasites --- and now she has passed on the information to Keiichi.
When Rena further examines the scrapbook, she discovers evidence implicating none other than Mion's family in the conspiracy. One of her best friends, the future head of the most powerful family in the village, is guilty of conspiring to commit mass murder? Somehow I fail to believe that.
Soon, a friendly and well-meaning detective named Ooishi reaches out to Rena and she begins to tell him about the plot to spread a plague of parasites among the outsiders and Oyashiro-sama nonbelievers. Soon she begins to have disturbing visions of her friend Rika coming at her with a needle, supposedly containing the parasite or a cure, as Rika claims. By now, thanks to Ooishi's help and his own common sense, Keiichi has learned the truth: Takano's conspiracy theory is just that, a theory, and the fact that everything seems to make sense is pure coincidence. However, Rena is too far gone to realize this.
The evidence she finds as she reads deeper and deeper into Takano's scrapbook continues to drive Rena to the brink of her sanity. What's more, Ooishi reveals to her a secret of Keiichi's: that he used to attack little girls who went out walking at night with a model gun. Enraged, she severs their friendship and leaves him distraught over their strained-by-deception relationship.
Now Keiichi must enlist the help of their other friends to stop Rena from going off the deep end, having remembered events that he himself experienced in a previous story arc, which is supposedly impossible. The paranoia that Rena is feeling will almost definitely send her into a homicidal fit, just like the "him" of a previous alternate world. Now he has to stop Rena before she kills anyone else!
Things are beginning to come full circle, and things could not be tenser than they are right now in Higurashi! Ryukishi07 truly has truly created a masterpiece of psychological suspense.
-- David Gromer