 It completes the story began in "The Family Trade" of Miriam Beckstein's attempts to understand and explore the new worlds she has access to.As the title suggests, the existence of families with the power to "worldwalk" unknown to the Clan comes of importance in this book, as a shadow war to undermine the Clan continues.The story also includes Miriam's exploration of a third world largely unknown to the Clan, where Massachusetts is part of "New Britain" and the British monarchy fled to America; this nation has roughly Edwardian mores and 1930s technology.