At night at a crime scene at the side of the road, Ōishi Kuraudo explains to Irie Kyōsuke, who takes notes, that according to their first assessment, the victim clawed his own throat out with his fingers. Irie considers it a strange method of suicide, and Ōishi asks him if drugs could be involved. Irie confesses that he never heard of a drug that would make a person claw at his throat until he dies.

Kumagai Katsuya asks Ōishi about a piece of lumber; he replies that it appears that the victim swung it around. Irie remarks that the victim, whom he identifies as Tomitake Jirō, had several bruises on his body. Ōishi concludes that Jirō was attacked on his way home from Okinomiya. Irie suddenly wonders about Takano Miyo. He explains that he thought she was with Jirō. Ōishi ask Kumagai to check with their department to see if she was at home. He then adds for Kumagai to check with the local police to see if a female body has appeared. Irie asks Ōishi if he believes that Takano has also been murdered. Ōishi admits that he is not sure, but if she is not found, then Jirō and her will be "the fifth year." Ōishi explains that these are the mysterious deaths, "Also known as 'Oyashiro-sama's Curse.'"

Satoko laughs at a set of cards depicting a rope, a gun firing, a syringe, and a bottle of poison as she announces that the syringe holds all of the hints to the mystery. Keiichi growls in frustration back at her as they play a card game with Mion, Rena, and Rika. Chie Rumiko enters the room, apologizes for the interruption, and tells her that she has a visitor.

Outside, Ōishi greets her at the doorway as "Ryūgū Rena-san, Ryūgū Reina-san." He shows his identification and suggests that they talk in his air conditioned car. In the car, he shows her a picture of Jirō and asks her if she knows anything about him. She recognizes him as well as a picture of Takano. He asks her the last time she saw them, and she responds that it was during the night of the Watanagashi Festival. He asks her if she noticed something unusual, and when asks him if something happened to them, he does not respond.

At home, Rena opens her desk drawer that contains Takano's three scrapbooks. In a flashback, she encounters Takano at the Shishibone Municipal Library. Takano reveals that she is researching the serial deaths and is certain another will happen. She asks Rena if she knows about the belief in Oyashiro-sama. She then theorizes that the "Curse" is carried about by fanatical believers. "Ever since the village's name change to Hinamizawa, many longtime Onigafuchi Village customs have ceased," she explains, then suggests that these fanatics are trying to rekindle some of the customs to "bring back fear of the name 'Onigafuchi.'" She suggests these fanatics include members of the three great families. With a giggle, Takano repeats the legend of Onigafuchi Swamp: demons emerged from it and attacked the village. Oyashiro-sama calmed down the demons and gave them human form so they could coexist with the village. Takano asks Rena what she can deduce from the legend. Rena looks embarrassed then reveals that she has met Oyashiro-sama.

Rena explains that before she entered grade school, she lived in Hinamizawa, but her mother's work led the family to live in Ibaraki. She pauses, and Takano suggests that Rena broke Oyashiro-sama's "taboo" of not leaving Hinamizawa. Rena agrees and continues that "a lot of bad things happened," over flashbacks her mother meeting her over an ice cream treat to her breaking windows at her school. Rena looks at two scars on her left wrist and admits that she sometimes cut herself. When she did, maggots would come out of with the blood. As her voice grows fearful, Rena explains that the maggots tried to crawl back into the wound. She admits she scratched at the wounds trying to dig out the maggots.

Takano gently stops Rena scratching at her scars, and Rena returns to the present. As she calms down, Rena admits that that is when Oyashiro-sama appeared and spoke to her. Rena explains that Oyashiro-sama warned her that the only way for Rena to survive was to return to Hinamizawa. Takano gently responds that she chooses to believe Rena. She then produces her three "treasured" scrapbooks which she offers to lend to Rena, the she asks Rena to keep her research and scrapbooks secret. Laughing, Takano suggests that if "those guys (連中・れんぢゅう・renchū)" discover her research and scrapbooks, she will be "erased." When Rena asks, "Those guys?" Takano merely laughs and leaves, and the flashback shifts to Ōishi in his car explaining to Rena that Jirō and Takano died.

Returning to present time, Rena opens one of Takano's scrapbooks to a page titled "Concerning 'Homing Instincts' and 'Home Sickness' (「帰巣性」と「ホームシック」について・"Kisōsei" to "Hōmushiku" ni tsuite)." She flips through some pages and arrives at "Maggots and Oyashiro-sama's Curse." She stares at the pages in fear.

Keiichi walks along the road to find a hand waving to him from the bushes. The blue wrist collar suggests that it is Rena. He walks over to the bushes only to have her hand grab his collar and pull him into the bushes. When he tries to protest, Rena clamps her hand on his mouth and hushes him. Rena looks about suspiciously, then tells Keiichi that she is being watched. Keiichi asks if it is by the police. Rena does not know, but she fears that it has been since the Watanagashi Festival. She reveals to Keiichi that she thinks people are after Takano's scrapbooks, and that she and Jirō were murdered. Keiichi protests that no one knows of this, and Rena suggests that the police are keeping their deaths quiet as they investigate. She believes they died because of her research.

She explains that Takano discovered an "important secret" concerning Hinamizawa. When Keiichi asks what it is, Rena admits that she has only read a bit of Takano's scrapbook and has much she needs to verify. A car driving down the road interrupts them. It is a white van. Keiichi asks if they are the ones watching her; Rena believes it is possible. She reveals that she has seen the white van several times on a street that rarely has traffic. Keiichi apologizes and affirms that he wants to help Rena, but he does not understand "the whole story." Rena suggests that the people who killed Takano and Jirō are part of the three great families: "To be more specific, Mi-chan's family, the Sonozaki family." When Keiichi protests, Rena reminds him of the serial mysterious deaths. She repeats Takano's suggestion that they all happened to revive belief in Oyashiro-sama. When Keiichi asks why Takano died, Rena suggests that it had to do with a secret shared by the three families. If it is reveals, "then the sacredness of Oyashiro-sama will be lost."

Keiichi asks what is the important secret. Rena demures that she needs more time to verify it. Keiichi accepts this, and Rena asks him not to tell anyone, especially Mion. After she leaves, Keiichi wonders to himself that if the Sonozaki Family is involved, then that suggests that Mion is as well. He quickly dismisses this. As he walks back to the road, he sees the white van stopped on the road. The passenger dressed in a grey uniform and sporting a ponytail asks Keiichi if he is on his way home from school. When Keiichi responds that he is, the man asks if he saw a girl. His description matches Rena. Keiichi denies that he saw her. The man tries to pass it off that they passed a girl but now see the boy Keiichi. His banter does not convince Keiichi: he concludes that they are the ones after Rena.

At home, Keiichi talks to Rena on the phone and asks her to tell him what in Takano's scrapbook lead to her murder. Rena responds that if what Takano wrote is true, then Oyashiro-sama will be diminished. Looking at an open scrapbook, Rena explains that those trying to revive belief in Oyashiro-sama had to keep this truth a secret. "In other words," Rena explains, "Oyashiro-sama is not a god." ]]

She continues that there are many teachings from Oyashiro-sama all based on the principle to not leave nor let others into Hinamizawa. Rena rhetorically asks him why Oyashiro-sama was born: "That's because demons emerged from Onigafuchi Swamp and attacked the villagers." However, Rena claims that this is a misinterpretation: "The demons didn't emerge and attack the villagers." Instead, if a human touched what came out of the swamp, that person became a demon who attacked people. When Keiichi asks "what" emerged, Rena replies, "Parasites!" She explains that it is a "bizarre, contageous disease that emerged from the swamp." The parasite renders the person insane. Keiichi wonders if Oyashiro-sama was really a doctor who came from a foreign country.

Rena replies that she cannot be certain, but "someone who can be referred to as a doctor," might have tried to treat the disease. However, they could only contain (対症療法・たいしょうりょうほう・taishōryōhō) the disease. To prevent the spread of the disease, the villagers created the rules that no one may leave and no one may enter: "It seems the parasites can only survive in Hinamizawa due to the temperature and climate." When someone tries to leave Hinamizawa, Rena explains, the parasites cause severe symptoms to stop them. This interference from the parasites is Oyashiro-sama's Curse. Keiichi protests that, nowadays, people enter and leave Hinamizawa. Rena explains that that is because Oyashiro-sama's plans worked. Sealing the village from outsiders lessened the danger of the parasites. If a person went outside, went insane and killed someone, that person was killed along with the parasite. Only parasites and people compatible with one another survived. This, Rena concludes, explains the mixing of "demon" and human blood.

The Watanagashi Festival involved the eating of the intestines of those who went insane. When she claims this was necessary, Keiichi asks if this was for vaccination. Rena laughs and compliments him for being smart as she thought. She claims it was "not that barbaric," but they created vaccines from those who died to bolster the resistance of the villagers. For those who worship Oyashiro-sama, "this theory can be disturbing." Keiichi agrees, and Rena continues that if the worshipers of Oyashiro-sama succeed, "they will revive a highly dangerous parasite." Keiichi wonders if the goal of this organization is to spread the parasite all over Hinamizawa. Rena believes that that is the case. When Keiichi asks if Mion is involved, Rena responds that she does not know if either she or Rika are. Nevertheless, even if they are not involved, if they learn of it, they may be in danger. Rena adds that she is glad that Keiichi is on her side. Keiichi reminds her that they are friends. Rena thanks him.

In school, Chie Rumiko helps some of the young girls. Keiichi works with Mion and Rena. Keiichi scolds Mion that she is calculating a math problem incorrectly. Mion looks confused and embarrassed, turns chibi, and complains how tedious it is. Rena looks out the window and notices though the window next to Tomita Daiki and Okamura Suguru the white van slowly drive by and stop. While Mion excitedly declares that she understand the math problem, only to be corrected by Keiichi, Rena continues to stare at the van.

In the school's Staff Room, Chie leave work to Okonogi. He thanks her and then produces a manilla envelope which he hands to her. As she places it on her desk and offer to show him the way, Rena peers through the door. After Chie and Okonogi leave the Staff Room, Rena sneaks in to look at the envelope. It contains the information for "Okonogi Landscapers." Rena tries to call the phone number on the envelope, but the number is not in service. "As I thought," Rena concludes, "they're. . . ."

The scene shifts back to the classroom before she finishes her statement. Her school bag remains on the hooks of her desk. Chie asks the students if any heard about Rena leaving school early. Rika gives a "Mi," and Mion shakes her head. Keiichi finds this disturbing.