Wow this was fun. I couldn't stop reading. Picking up from the events of the first book, we have sort of a standoff between the three contenders for the crown. Katharine the poisoner queen has come back changed from the events of the Quickening, and man is she ever changed. Almost not even the same character. Arsinoe the naturalist queen has a secret that I won't reveal, and Mirabella the elemental queen is considered the strongest of the three. Nothing is settled though- each contender still has their faction firmly behind them, and so the struggle continues.
There are a lot of characters in this book, and even though I took some notes when I read book one, I still had a few things I didn't remember. For the most part though the story continues seamlessly and the characters continue to impress. It's not just the three queens who are compelling- the supporting characters, like Billy and Jules and others, are as well. One thing about the first book is I had a hard time picking a favorite, and indeed didn't really have one. That changes here, as things get a little more ruthless and I was definitely pulling for one (or two) of the sisters over the other. There are story reasons for that, and in fact the central mystery of the book is specifically bound up with one of the sisters.
As far as the mystery itself, much like the first book we are given bits of information but a lot remains unknown. It's clear that this mystical island has a lot of secrets, and the factions and queenly traditions are so rigid and bloodthirsty that one wonders what started all this. I expect that in the next two books we're going to learn a lot more about the island, what it actually is, and why the queen selection process seems so odd. I would have preferred more answers, but I still enjoyed this a great deal. The pace is fast and frankly I thought this one got going a lot quicker than the first one.
It's hard to say too much more because of spoilers, but suffice to say that if you enjoyed the first book you are probably going to like this. I loved it and blew through it. This is fast becoming a favorite series, and there's a lot more action in this one too. This one was superior to the first one for me, and the moral quandaries they face- do you kill your sisters to win a throne, just because that's what has always been done- were handled well.