The narrator in Part 1 is a man named Mr. Cheong who (though himself nondescript) characterizes his wife, Yeong-hye, as "completely unremarkable in any way." Mr. Cheong always strives to take the middle road in life by choosing not to stand out. This—alongside his expectation of his wife's total submission—causes him to be at a complete loss when Yeong-hye suddenly becomes vegetarian. Yeong-hye speaks in brief dream-monologues as she describes the grotesque nightmares that fuel her decision. Mr. Cheong becomes increasingly angry at his wife's behavior as she refuses to wear a bra, eat meat, or actively engage in conversation with Mr. Cheong's colleagues. This culminates in sexual violence when Mr. Cheong rapes Yeong-hye.
Eventually, Mr. Cheong involves the rest of Yeong-hye's family in an effort to control her. They gather at Yeong-hye's sister's house for a family lunch. Yeong-hye's father, a military veteran with a brutal temper, physically strikes his daughter and attempts to force-feed her pork. Yeong-hye brandishes a knife at her family members before slashing her own wrist, after which she is rushed to the hospital.
Part 2, "Mongolian Mark," takes place two years after Yeong-hye's hospitalization, and is narrated by her brother-in-law. He is never given a name, but the reader learns he is a video artist. After his wife, In-hye (Yeong-hye's sister), offhandedly remarks that Yeong-hye still has congenital dermal melanocytosis, the narrator is gripped by an erotic image. His idea is to film two people having sex while painted all over with flowers. This idea stems from a fantasy of himself violently having sex with Yeong-hye.
The narrator successfully convinces Yeong-hye to be a part of the erotic video project, and he recruits another artist named J. However, J underperforms during the filming process, and the narrator succumbs to his desire to be the male counterpart in his vision. Part 2 ends with In-hye discovering her husband in bed with her sister the morning after filming the video. In-hye subsequently calls emergency services as a result of the disturbing transgression.
In-hye narrates the third and final part of the novel, "Flaming Trees." Part 3 takes place one year after the events of "Mongolian Mark," though it often flashes back to recount past events and perspectives (such as the sisters' childhoods as well as what drove them both to their failed marriages). In-hye details Yeong-hye's deteriorating mental state as well as her own stress and exhaustion. In-hye has become her sister's sole support since the rest of the family abandoned them. In-hye regularly visits her sister at Ch'ukseong Psychiatric Hospital, hoping that she will eventually recover. Towards the end of the novel, however, Yeong-hye claims that she is no longer a human or even an animal, but rather, a plant. She becomes non-verbal and stops eating altogether. After a final attempt by the nurses at Ch'ukseong to force-feed her, In-hye, witnessing the scene unfold, bites the arm of a nurse and prevents the procedure from taking place. The doctors send the sisters to another hospital by ambulance, as this is the only hope to save Yeong-hye's life. The novel closes with an ambiguous scene in which In-hye gazes defiantly through the window at the sunlit "flaming" trees rushing by.
