The story follows the adventures of the Waterbury children, who are forced to move with their mother (Dinah Sheridan) from a luxurious Edwardian villa in the London suburbs to "Three Chimneys", a house near the fictional 'Great Northern and Southern Railway' in Yorkshire, as their father (Iain Cuthbertson), who works at the Foreign Office, has been imprisoned as a result of being wrongly accused of selling state secrets.