Throughout The Thirteenth Tale, Setterfield explores the bond between twins and the effect of their separation. She illustrates this through the relationship between the Angelfield twins, Emmeline and Adeline, as well as through Margaret and her dead twin, Moira. The fact that both Vida and Margaret are, in Margaret’s words, “lone twins” is what finally convinces Margaret to take the job as Vida’s biographer, placing this theme firmly as a central concern of the novel.

At Angelfield, Emmeline and Adeline live entirely in their own world during their childhood. As the Missus says, “They don’t know that anyone is alive but themselves” (83). The twins live in a self-contained world until Hester comes to Angelfield, and to her, it even seems as though they are each one half of a whole person: “Where an ordinary, healthy person will feel a whole range of different emotions, display a great variety of behaviors, the twins, you might say, have divided the range of emotions and behaviors into two and taken one set each” (178). Emmeline has a healthy appetite, is quiet and docile, and shows interest in her schoolwork, while Adeline is thin and never eats, wild, violent, and withdrawn. In fact, Hester undertakes the separation of the twins because of her suspicion that Emmeline’s presence is hindering Adeline’s development.