Aristocratic, impoverished and reclusive, with a truly historical lineage, Lord and Lady Brocklebank live in the magnificent but decrepit Longleigh House with their mentally challenged son James. Close to bankruptcy, Donald is negotiating to sell the family home when Nancy is taken seriously ill. In order to pay for her operation, Donald has to leave the estate for a few days and so arranges for the family nurse to take control. James however wants to prove to his father that he is a responsible adult and perfectly capable of looking after his mother. As it becomes less and less apparent who is ill and who is not, what is real and what is not, the unimaginable becomes imaginable and the nightmare begins.