Seraphine Mayes and her brother Danny are known as the summer-born Summerbournes: the first set of summer twins to be born at Summerbourne House. But on the day they were born their mother threw herself to her death, their au pair fled, and the village thrilled with whispers of dark-cloaked figures and a stolen baby. Now 25, and mourning the recent death of her father, Seraphine uncovers a family photograph taken on the day the twins were born featuring both parents posing with just one baby. Seraphine soon becomes fixated with the notion that she and Danny might not be twins after all, that she wasn't the baby born that day and that there was more to her mother's death than she has ever been told. Why did their beloved au pair flee that day? Where is she now? Does she hold the key to what really happened?