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.

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.