One of the biggest problems with a book you can't put down is that once it's done, you have THAT MUCH LONGER TO WAIT until you get the next one. I suppose you could say it's a good problem to have, but it also REALLY sucks at first!
Toby is gaining something of a reputation thanks to her actions over the past eight books, so when the threat of war comes to the kingdom, she gets involved in spite of herself. The leader of the kingdom is young and new, but I think she has a good head on her shoulders once she focuses. So, with backup in the form of fiance Tybalt, squire Quentin, fetch May and regular minor recurring character and alchemist Walther, she heads up to the offending land as a diplomat hoping to head off the war.
Yeah. Toby Daye, diplomat. If you're familiar with this series, just let that sink in for a few seconds.
The Kingdom of Silences might be one of the creepiest things McGuire has ever crafted in this series - in any series I've read of hers, actually, including Feed. It's a totalitarian place, focused on an unnerving sense of "purity" - not just on blood purity (May is reduced to tears when she finds out how changelings are treated, and Toby is clearly also bitterly angry - especially when that attitude is extended to her. But that's not all. The court is also terribly homogenous as far as what sort of fae are there, and how they're kept in line (there's fear, but there's not JUST fear). And then there's Walther's particular connection with the kingdom and some of the people there.
Basically, we find out pretty fast why the kingdom declared war, and it's every bit as despicable and horrible as we imagined from the start and from the way the court is kept. But Toby being Toby, she keeps trying to do her job, and Tybalt is there to back her up. There's way less action in this book than in previous ones, but it's replaced with a horrible tension. And I don't mean horrible like badly written, but like that underlying sense of dread that comes from wondering what is going to happen next - or basically, what the leader of the Kingdom of Silences, Rhys, is going to do next. There comes a point where you realize there's pretty much nothing you can't see him doing to get what he wants, and that's terrifying.
Now, it's definitely not my favorite book in the series, and I don't even think I like it as much as the last one within its world. It has a few flaws. For instance, one of the problems I had with the last book was that two of my favorite characters got backseated, and it happens again here. May and Quentin are both there, and of the two May feels more like she has an impact on the story. But Quentin... *sigh* I think he was in the book more in the form of Toby worrying about getting him hurt or found out than in him actually *doing* things. I can't remember a single thing he did in this book was indispensible to the tale, making him a superfluous addition who felt like he was there solely because he had to be as Toby's squire. I found it disappointing, since it felt like a step backward for his character.
But that doesn't stop that the book as a whole is relentless and gripping even as it's horrifying. Even a couple fantastic new character in the Portland King of the Cats and another blodynbyrd aside from Luna can't really break up the thick fog of what-happens-next that had me in a stranglehold.
In all, don't start here. You could probably get on that way, but you're going to miss a lot and some of the things they can do aren't really explained so well in terms of their impact on characters and plot previously. But maaaaan, if you are in this series already, I think this is a fantastic book, and as mentioned at the start, I had a really hard time putting it down.