This is the last book of the Kate and Cecy Regency themed books that happen to involve magic. (It’s ten years later, so this one actually takes a bit of a steam punk turn.)
Cecy, and her husband James, have been asked by the Prime Minister to investigate the disappearance of a German magician who was hired to look into some railway problems up north. That means that Kate will take Cecy’s children, including her rather rambunctious twins, in with her own, at the family estate.
James and Cecy find some highly irregular ley line formations on the path of a new railway, which seem to be effecting how the railway works. Meanwhile, someone is trying to break into Kate’s home, and one of the boys goes missing. He’s quickly found, with a girl of obvious high born status who refuses to speak because she’s afraid that saying anything will hurt her mother.
Like the other books, this one is told as a series of letters between Kate and Cecy, as well as between James and Kate’s husband Thomas. They’re as mad cap as ever, and it was a fitting end to the series.