The remoter parts of the English Fens are forlorn, lost and damp even in the height of summer. At Iyot Lock, a large decaying house, two young cousins, Leonora and Edward, are parked for the summer with their ageing spinster aunt and her cruel housekeeper. At first the unpleasantness and petty meannesses appear simply spiteful, calculated to destroy Edward's equanimity. But when spoilt Leonora is not given the birthday present of a specific dolly that she wants, affairs inexorably take a much darker turn with terrifying, life-destroying consequences for everyone.