As per usual, I am going to refrain from posting the synopsis so that I don't ruin the first two in the series for anybody tempted to pick these up - if either you've read Storm Glass and Sea Glass and are yet to get round to Spy Glass or are just not that bothered about spoilers, check out the book on GoodReads here.
I'm always wary of final books in any kind of series, be it 3 or 13 books, because by that point I've already invested a lot of time in the characters and have usually come to love some or all of them. I worry that the author will throw a curve ball that I won't like and that it will taint my views of the previous books or that the ending won't be one that works or that they will try too hard and rush things in an artificial finale. That said, I'm not much of a worrier, honest!
To her credit, Snyder falls into none of these traps and I loved the final book of this series. It's fast-paced and ties together the characters, countries and their pasts without seeming strained. What I found amazed me the most was how, when I finished the book with a tear in my eye (not always hard to produce...), much I loved the ending. If I'd been told the ending while reading the beginning of the series, heck, even the beginning of this book, I would have been disappointed, I think. But the story is so well drawn and the characters so well woven that I found that it was exactly the ending I wanted by the time it came around!
Which relates nicely to one of the best things about this, and Snyder's other, book(s). The characters are just fantastic - they're intriguing and surprising and grow as you're reading. Opal in particular has become a lot more worthy of her role as lead female and has lost a lot of the petulance that seems to cling to her in Sea Glass. Even better, my favourite character from the Study series returned to this one so I was a happy girl!
Also, on a more serious(ish) note, I respect Snyder for using the often frivolous fantasy genre to look at some challenging socio-political issues. Admittedly, I could be over-analysing but I have got the impression before that there is a lot more than meets the eye to some of the trilogies' mechanisms (for example, capitalism v communism). Without revealing too much (I hope), Opal finds herself in an extremely patriarchal (bordering on cultish) society and looking at the plight of the repressed masses when in the thrall of a man who is, to all intents and purposes, a dictator. It's disturbing and in some ways abhorrent and the scariest thing is, it has at some places and in some times been some people's reality. You could quite easily read these books without looking at them in this way but I think it adds something to the story that is unique, refreshing and intelligent. As I said though, it wouldn't be the first time I've over-thought something...
Overall: I definitely recommend this series to fans of fantasy fiction - there is a light-hearted wit running through the book but the events are often harrowing, which is a welcome contrast. It has action, romance, magic, political intrigue and scandal - what's not to love?! Go grab a copy of Storm Glass and get going - you won't regret it!