Still reeling from tragedy, the Moorcroft family leaves London for a remote Scottish island only to find their problems increase tenfold.
Thirteen months earlier, one of Sarah and Angus' identical twin daughters, 6-year-old Lydia, died following a freak accident. Tremayne explores the circumstances of Lydia's death in retrospect as the novel alternates between Sarah's first-person perspective and less-effective third-person chapters focused on Angus. No longer the picture-perfect family, all of the Moorcrofts buckle under the strain of grief: Angus' increased drinking leads to a blowup at work and the subsequent loss of his job; Kirstie, Lydia's twin, is withdrawn and friendless; and Sarah is barely hanging on to her sanity. Then Kirstie tells Sarah something shocking and, for readers, requiring a healthy suspension of disbelief: "It was Kirstie that died. I'm Lydia." The revelation causes Sarah—she doesn't share Kirstie's secret with Angus—to re-evaluate everything she thought she knew about the accident and its aftermath. Looking for a fresh start, Angus and Sarah decide to leave London and start anew in a dilapidated lighthouse cottage on Eilean Torrran, a tiny Scottish island accessible only by boat. This is wise only in that it furthers the increasingly audacious plot—for the characters' mental health, it's a terrible idea.
Tremayne ably spins numerous variations of the which-twin-is-really-dead idea, playing into the inherent creepiness of wholly identical twins like Kirstie and Lydia, indistinguishable even on a DNA level.