In the windswept British seaside town of Ridinghouse Bay, single mom Alice Lake finds a man sitting on a beach outside her house. He has no name, no jacket, and no idea how he got there. Against her better judgment, she invites him inside.

Meanwhile, in a suburb of London, newlywed Lily Monrose grows anxious when her husband fails to return home from work one night. Soon, she receives even worse news: according to the police, the man she married never even existed.

Twenty-three years earlier, Gray and Kirsty Ross are teenagers on a summer holiday with their parents. The annual trip to Ridinghouse Bay is uneventful, until an enigmatic young man starts paying extra attention to Kirsty. Something about him makes Gray uncomfortable — and it’s not just because he’s a protective older brother.

Who is the man on the beach? Where is Lily’s missing husband? And what ever happened to the man who made such a lasting and disturbing impression on Gray?