A year after one of their twin daughters, Lydia, dies in a terrible accident, Angus and Sarah Moorcraft are on the verge of bankruptcy and make the life-changing decision to move to a tiny Scottish Ireland Angus has inherited from his grandmother. But the move is fraught with difficulty, particularly as the Moorcrofts surviving daughter, Kirstie, seems to be having a delayed reaction to her twin sister's death, claiming that she is in fact Lydia and it was Kirstie who died. As winter encroaches, the fog rolls in, bringing with it a creeping atmosphere of unease. Angus is forced to spend more and more time away from the island for work, Lydia is having trouble making friends at school and Sarah is feeling more and more isolated. When a violent storm leaves Sarah an Kirstie completely stranded and alone, Sarah finds herself tortured by the past — what really happened on that fateful day her daughter died?