The five girls' problems with supernatural beings have been solved, and it's now summer break, with the culture fair over. Koyomi Araragi has two little sisters, self-proclaimed "heroes" nicknamed the Fire Sisters, Karen and Tsukihi.

Temptation haunts Koyomi, while visiting Sengoku he is presented with several tempting offers. After surviving each one, his visit to Kanbaru continues to put him in compromising situations.

Araragi leaves Kanbaru's house and meets a dangerous man named Kaiki. While following him, he runs into Senjougahara, who berates him for skipping his studies.

Karen is badly ill, having been poisoned by an evil, supernatural bee. Will Koyomi be able to cure her in time?

Koyomi learns the whole story about what happened between Karen and Kaiki. After receiving a tempting offer from Hanekawa, he speaks with Shinobu on the way to save Karen.

Koyomi leaves Karen behind at home to talk with Senjougahara. Senjougahara seems to be planning on confronting and murdering Kaiki. When he comes back home, he learns Karen has wandered off, while still sick.

Araragi goes to confront Kaiki and stop him from leaving the city. But Kaiki is wiley and smart, and not easily dissuaded when there's money on the line.

Karen is acting clingy and very cute, completely out of character. But its a trick to get Koyomi to introduce her to Kanbaru. In response, he devises a test Karen must pass; a test involving her toothbrush.

While taking Karen to meet Kanbaru, Araragi is put into a compromising position. On the way, he runs into someone asking about familiar things.

Araragi agrees to take Shinobu on a trip to buy doughnuts. At the restaurant, an old acquaintance is able to give information on the town's new visitors.

As Shinobu explains how Tsukihi came to be in her currents situation. Araragi resolves to stop the out-of-towners from killing her. But unlike Oshino and Kaiki, Kagenui speaks with her fist and she talks a lot.

Koyomi and Ougi find themselves trapped in a classroom, and the story shifts back to the point when Suruga introduces Ougi to Koyomi. Ougi approaches him with a mystery about a room not seen in the school's blueprints for them to investigate. When they enter the room, they find themselves trapped inside, leading them to their current situation. While talking about their predicament, the duo realize that the room is an oddity created by a traumatic memory from Koyomi's freshman years. Koyomi then tells Ougi that two years prior, the class president at his and Hitagi's class at the time, Sodachi Oikura, was looking for possible culprits of cheating on a math test, and would not allow any student to leave class until a culprit was found. Ougi surmises that they themselves won't be able to leave the room until the two-year-old mystery is solved.

In the aftermath of the previous day, Araragi is about to enter his classroom when Hanekawa informs him that a student absent all year is finally attending. The story pushes further into the past, as more of “what” makes Koyomi Araragi is revealed.

Having rediscovered the room on the second floor of the ruined house, Koyomi tells Ougi of the events that happened there five years earlier.

Hanekawa reveals her concerns about Ougi as she and Araragi go to visit Oikura.

Araragi and Hanekawa visit Oikura and learn the painful story of her family's past.

Ougi claims to have figured out the whereabouts of Oikura’s mother and, in her own way, helps Araragi and Hanekawa to solve the mystery.

Koyomi Araragi waits in the ruins of the cram school to ask Suruga Kanbaru for help, a request he hopes she will refuse.

After a hurried departure from the cram school ruins, Koyomi and Suruga head toward the meeting place, only to encounter some difficulty along the way.

Having finally arrived at the meeting place, Koyomi and Suruga find an unexpected person waiting for them. Before their reunion can take place, they must face an unexpected foe!

The group relocates to the North Shirahebi Shrine where Izuko Gaen tells them the story behind the location and the effect Shinobu's first minion had on it.

Koyomi is confronted by Shinobu's first minion, the original apparition killer. But instead of starting a battle, the samurai makes a simple request.

As Koyomi prepares for his duel, he learns of the crisis that Hanekawa is facing and must decide what battle he should fight.