In a wintry seaside resort an old woman goes missing from her residential hotel for the elderly, the inappropriately named Happy Haven. And in a remote farmhouse not far away, the Moon family gathers for its traditional Christmas. Clover Moon, the farmer's wife, knows that her mother-in-law, Violet, regards her as an inadequate and unsuitable wife for her beloved only son. But would she actually go so far as to try and kill her? And what are the dark secrets in Violet's past? As gales and blizzards cut off the power and maroon the Christmas gathering, where did the body come from which is swept into the farmhouse cellar by the rising floodwater?