The chapters of the book switch between the past and present day life of the two main characters (Margaret Lea, Vida Winter). At the novel's inception, Lea divulges her work in her father's antique book store, her one-time jaunt as an amateur biographer, and her chance discovery at age 12 that she was born a conjoined twin, her sister dying shortly after their separation. This discovery has caused her pain and provided a reason for longing she felt before that, as does her strained relationship with her mother, who became depressed and withdrawn after the twin's death. After the character of Vida Winter is introduced, she narrates sections of the book, in sessions with Lea in her library. Given Winter's detailed and vivid account of her past, Lea later finds it easy to write a narrative from her notes. This becomes the biography that Winter commissioned Lea to do.
The story of Winter's history is at first written in third person past tense, but at a turning point in the story, when Charlie is missing, Winter suddenly uses the pronoun "I". This is explained later in the book when Lea understands all the secrets of the March family. The rest of the book switches from the present Lea, who tries to fight her own ghosts and discover the secret of the March family, whilst the other is the story of the Marches seen through the eyes of Winter.
The switches between character narration and the story of Winter is marked by a graphic that clearly show which character is narrating that section of the chapter. It is also made more obvious by the lack of dialogue. When the narrative is about the past, dialogue is rarely shown. There is more dialogue when the story is located in the present; particularly between Lea and Aurelius.