After escaping London and a career that nearly destroyed her, Justine plans to spend her days doing as little as possible in her beautiful home in Devon. But soon after the move, her daughter Ellen starts to withdraw when her new best friend, George, is unfairly expelled from school. Justine begs the head teacher to reconsider, only to be told that nobody's been expelled - there is, and was, no George. Then the anonymous calls start: a stranger, making threats that suggest she and Justine share a traumatic past and a guilty secret - yet Justine doesn't recognise her voice. When the caller starts to talk about three graves - two big and one small, to fit a child - Justine fears for her family's safety. If the police can't help, she'll have to eliminate the danger herself, but first she must work out who she's supposed to be.