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 10 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and provided a reason for longing she felt, and for her strained relationship with her mother, who became depressed and withdrawn after the twin's death.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 from Lea.