Where is the line between hope and madness?

Stella and her boyfriend were teenagers when their one-year-old daughter, Alice, vanished during a holiday. Though her body was never found, Alice was assumed to have drowned. Twenty-one years later, Stella is happily married and a successful therapist. But everything falls apart when a new patient walks into her office. The young woman introduces herself as Isabelle - but Stella is sure she's Alice.

But when no one believes her, Stella begins to doubt her own mind. Even when her life is threatened, she can't convince anyone the danger is real. But for the chance to get her daughter back, Stella will risk anything: her licence, her marriage, her life. And in doing so, she'll confront a series of chilling questions. What happened on the beach all those years ago? If Alice is alive, why has she come back now? And how far will Stella go to save her?