The Crowded Shadows is the perfect middle book;* its got all of the things you'd expect from a middle book, and not many of the things you wouldn't. It probably wouldn't stand on its own, it helps to flesh out the characters and build tension leading up to the finale, the stakes get higher, and some of the mysteries of the the first book get resolved.
Sort of. And not all of them.
Celine Kiernan does write a pretty good story. The characters are solid and feel like people, and only occasionally does someone say or do something that seems slightly out of character. Seems hard to keep track of that as a writer, but there you are.
In this series you've got your swashbuckling, your horse riding, your royal court intrigue, mystery as I've said, and speckled throughout, you've got your religion and religious fanaticism, you've got your love, your hate, and your love-hate relationships, your mysticism, occult, and a few talking animals.
A little something for everyone.
On to the last book!
* I've called these bridge books in the past.