Widowed Mrs Martingale (Cicely Walper) and her four children – Petronella (Elizabeth Saunders), Nicholas (Wilfred Downing), Dinah (Caroline Denzil) and Benjamin (Colin Gibson) – inherit a castle in the will of an elderly relative. When they move in they find dear old Miss Button (Evelyn Moore), the housekeeper, a whole host of cats and, odder still, a boy called Christopher Sixpence (William Simons) who keeps appearing and disappearing. What is he doing there?