As he prepares to go to the funeral of Otsutarō Hashizuka, narrator Tomohiko remembers events from 16 years before, when he was a junior in high school. He had been living with Otsutarō and his daughter Nao for the previous four years, ever since his mother had abandoned the family and his father was transferred to the corporate office in Tokyo; when Tomohiko balked at leaving the coastal town where he grew up to move with his father to Tokyo, his next-door neighbor Otsutarō had offered to take him in. When Tomohiko was in fourth grade, Otsutarō had lost his wife Itsuko and their sixth-grade daughter Sayo as the result of a tent fire while camping. Itsuko died from the burns she suffered while rescuing her daughters, and Sayo killed herself six months later in despair over the keloids that covered half of her face. Tomohiko had been drawn to the stoic and strong-willed Sayo from when he was small, and blamed her suicide on an ill-considered remark he made to her about getting married when they grew up, not realizing it would come across only as pity.
As a high-school student Tomohiko helped Otsutarō in his termite extermination business. While handling a job for an elderly man named Watanuki, he learns that a woman who bears a strong resemblance to Sayo frequents his house. Curious about their relationship, he sneaks into the crawl space at night and hears them making love. Then one night when he is in the crawl space, a fire breaks out and he barely manages to escape with his life. The house burns to the ground, and Watanuki is killed. Tomoko?the woman who looks like Sayo?tells Tomohiko that he has saved her by killing Watanuki; he begins going to see her at her apartment, looking forward to each rendezvous. But then one day he catches Tomoko having sex with Otsutarō. She explains that Otsutarō forced her into it by threatening to reveal how the house fire got started: although Tomohiko thought Tomoko had set it, she believed he had done it, and she had submitted to Otsutarō in order to protect him. Tomoko also confesses that when she went camping in high school, a cigarette butt she tossed aside had set someone’s tent on fire, and it was under the threat of being exposed by Watanuki, her teacher at the time, that she had gotten involved with him. Realizing she is the one responsible for burning the Hashizuka family tent, Tomohiko calls her a murderer and leaves.
Two years later, on a trip home from college in Tokyo, Tomohiko goes to visit Tomoko’s apartment, but finds her gone. Nao tells him that she committed suicide; she also reveals that Sayo herself had actually caused the tent fire?by playing with fireworks inside the tent.
Returning to the present, Tomohiko and Nao, now his wife, are headed for Otsutarō’s funeral. In the passing crowds on the way, he catches sight of Tomoko carrying a baby in her arms. Had Nao told him Tomoko was dead all those years ago just to make him forget her? And in that case, was her story about how the tent fire “actually” got started a lie as well? His eyes meet Tomoko’s, but he tears them away and looks down at Nao’s swollen belly, pregnant with their first child.