The Mislaid Magician or Ten Years After is the third book in a series constructed by the authors by writing letters back and forth to each other in character. It is now ten years after Kate and Cecelia found and married Thomas and James. Both couples have settled down to raise their families in peace and quiet. But when the Duke of Wellington asks James to find out what happened to a German engineer who was looking into problems with the new railway lines, there's nothing for it. Duty must be met, and James and Cecy drive off to look into the matter. But what starts out as a simple missing persons case quickly turns into magic, treachery, treason, and an ancient magic that binds and protects all of England.

(Source: Harcourt Children's Books)