Diane Setterfield’s The Thirteenth Tale is a mystery told in a story-within-a-story format. The framing device revolves around Margaret, a bibliophile and occasional biographer who works in a bookstore. One day, Margaret is contacted by the prolific writer Vida Winter, who asks her to write her biography. Vida is a successful novelist who has repeatedly invented outlandish stories about her background, adding significant mystique to the successful writer’s career. When Vita hires Margaret, she makes it clear that she will retain full control of the project.
The majority of the novel takes place in the past as Vita regales Margaret with the true story of her youth. In addition, Margaret does some amateur sleuthing of her own in light of Vita’s tendency to alter the truth. Vita reveals that she is actually Adeline Angelfield, who grew up in highly unorthodox circumstances on a country estate. The twins were the product of Isabelle, a disturbed woman who is eventually committed to an asylum, and Roland, her ineffectual husband. Also living on the grounds are Isabelle’s volatile and violent brother Charlie; John-the-dig, the groundskeeper; and the Missus, the elderly housekeeper who eventually develops dementia. The divergent nature of the twins is revealed during an extended sequence in which a governess is hired in an attempt to bring order to the household. Despite her efforts, she is unable to make progress with the wild Adeline and the withdrawn (and possibly challenged) Emmeline.
Margaret eventually uncovers that Adeline and Emmeline were likely the product of an incestuous relationship between Isabelle and Charlie. Furthermore, there was a third child, born out of Charlie’s rape of a nearby woman. Vita reveals that she is actually this child, not Adeline, and was kept hidden in the house much of the time. When seen, she was often mistaken for Adeline because they looked so similar and were close in age. The action climaxes when Adeline starts a fire and Vita is only able to rescue one of the twins. Since the surviving twin is badly burned, Vita is never sure which one died in the fire. At the end of her story, both Vita and her half-sister die. The novel ends with Margaret making peace with her own ghost: a conjoined twin who died after they were born.