In 1910, 11-year-old Iris Villarca lives with her father at Rawblood, a lonely house on Dartmoor. Iris and her father are the last of their name. The Villarcas always die young, bloodily. Iris knows it's because of a congenital disease that means she must be strictly isolated. Papa told her so.

Forbidden to speak to other children or the servants, denied her one friend, Iris grows up in solitude. But she reads books. And one sunlit autumn day, beside her mother's grave, she forces the truth from her father. The disease is biologically impossible. A lie to cover a darker secret. The Villarcas are haunted, through the generations, by her. She is white, skeletal, covered with scars. Her origins are a mystery, but her purpose is clear. When a Villarca marries, when they love, when they have a child - she comes, and death follows. Iris makes her father a promise: to remain alone all her life. But when she's 15, she breaks it. The consequences of her choice are immediate and horrific. Iris' story is interwoven with the past, the voices of the dead - Villarcas, taken by her.

Iris' grandmother sets sail from Dover to Italy with a hired companion, to spend her final years in the sun before consumption takes her. Instead she meets betrayal and a fate worse than death. Iris' father, his medical career in ruins, conducts unconscionable experiments to discover how she travels in the Villarca blood. Iris' mother, pregnant, walks the halls of Rawblood whispering to her, coaxing her to come. As the narratives converge, Iris seeks her out in a confrontation that shatters her past and her reality, revealing the chasm in Iris' own fractured identity. Who is she? What does she desire? The answer is more terrible and stranger than Iris could have imagined.