Two impoverished children, Edred and Elfrida Arden, inherit the decrepit Arden Castle and search for the lost family fortune that will allow them to rebuild it.
With the assistance of the magical Mouldiwarp, Edred and Elfrida travel back in time to earlier periods of English history, searching for clues.
Nesbit created an innovative body of work that combined realistic, contemporary children in real-world settings with magical objects - what would now be classed as contemporary fantasy - and adventures and sometimes travel to fantastic worlds.