This story takes place several decades before the Parasol Protectorate and only features three crossover characters (who will remain nameless so that I don't spoil the book). It follows Sophronia Temminick through her first term at a very odd finishing school that teaches young ladies of quality the skill and social graces needed to survive in the upper classes of English society. And how to employ those skill as an effective spy and/or assassin.
As with Ms. Carriger's other works, this book is well written with engaging characters, brilliant dialogue, and edge-of-the-seat plot. It expands on the world in which we met Alexia Tarabotti, delves into some of the history of world without spoiling the other books, and develops new, exciting elements make the world feel so much more realistic!
My only complaint is that suspension of disbelief is difficult for me when it comes to the finishing school itself. I don't want to ruin the surprise for any potential readers, and I did find the school to be very clever and fascinating, just rather difficult to accept as "possible," even within the realm of this extremely fanciful universe.
Overall, I think this is another book by Ms. Carriger that deserves a place on your bookshelf. And if you have a teenager in the house who may not be "old enough" to read the Parasol Protectorate, give them this one as it's appropriate for pretty much any age.