In her proem ‘The Fairy Melusine’, the fictional Victorian poet Christabel LaMotte – one of the central characters of A. S. Byatt's Possession – retells the medieval romance of Mélusine, emphasizing the beautiful fairy's seemingly paradoxical dual nature, made manifest in her weekly transformation into a half-serpent. What fascinates Christabel most about Mélusine is the richness of her character, as she is both ‘an Unnatural Monster – and a most proud and loving and handy woman’, or ‘a combination of the orderly and humane with the unnatural and the Wild’. Christabel is not the only one captivated by this medieval legend of a noble woman cursed to become an animal–human hybrid every Saturday – most of Byatt's characters are similarly entranced by Mélusine's ambiguous, multifaceted nature.

In this, the novel follows in a long tradition of artistic and scholarly fascination for the puzzling figure who is Mélusine. Indeed, there has been much critical debate on her true nature: some scholars see Mélusine as a benevolent fairy lover, some categorize her as a foundational ancestor or mother goddess figure, whilst others argue that her serpentine nature links her with demons, the Eden serpent or the monstrous races of sirens, undines, and succubi. However, Mélusine's character is so remarkably ambiguous and multifaceted that it is misleading to attempt to define her by one particular characteristic alone. Just as Mélusine's body continually changes – from human to hybrid and eventually to animal – so does her character, allowing for a multitude of possible readings.