Seraphine Mayes and her brother Danny are the first set of summer twins to be born at Summerbourne House, a crumbling manor on the Norfolk coast. But on the day they were born their mother threw herself to her death over the cliffs behind their house, their au pair fled, and the village thrilled with whispers of dark-cloaked figures, changelings and a stolen baby. Now twenty-five, Seraphine becomes fixated with the notion that she and Danny might not be twins after all.