Nina Landry has given up city life for the isolated community of Sandling Island, lying off the bleak east coast of England. At night the wind howls. Sometimes they are cut off by the incoming tide. For Nina though it is home. It is safe. But when Nina's teenage daughter Charlie fails to return from a sleepover on the day they're due to go on holiday, the island becomes a different place altogether — a place of secrets and suspicions where no one — friends, neighbours or the police — believes Nina's instinctive fear that her daughter is in terrible danger. Alone, she undergoes a frantic search for Charlie. And as day turns to night, she begins to doubt not just whether they'll leave the island for their holiday — but whether they will ever leave it again.