Two siblings, Edred and Elfrida Arden, inherit a crumbling castle and discover they are the last of an ancient noble family. With the help of a magical creature called the Mouldiwarp, they travel through time to find a lost treasure that will restore their family's fortune. Their adventures take them to different historical periods where they must solve puzzles and face challenges. The story explores themes of family, responsibility, and how the past shapes the present.