Excellent of its type. Of course, it is awash with the aristocrats and private incomes typical of the time, but don't be put off by that!
The plot is well constructed and the characters superbly drawn. What I liked most about it most was the lack of empty jingo, and the fact that the characters are not drawn in black and white. Even several of the villains have their redeeming features.
Pacey and written in a clean and surprisingly modern style, I read it in two sittings.