Atmospheric horror starring Maria Bello and Sean Bean. Adelle (Bello) is visiting her estranged husband James (Bean) with their troubled daughter Sarah (Sophie Stuckey), deep in the Welsh countryside. Tragedy strikes when Sarah is swept out to sea while on a trip to the beach, and while James desperately leads the search for her, Adelle starts to have strange visions of a young girl that hint towards Sarah still being alive, and trapped somewhere in the house. As Adelle investigates further, she learns of a sinister pagan community that lived in the area 50 years before, and all apparently committed mass suicide. Through the only survivor, Daffyd (Maurice Roeves), Adelle learns of a mythical underworld known as 'The Dark', where she believes Sarah might be trapped. When a traumatised young girl arrives at the house, Adelle starts to plan how she can get Sarah back. But who is this sinister young girl, and how far will Adelle go to reclaim her daughter from the underworld?