Opal gets kidnapped. She gets kidnapped in every book she shows up in, usually repeatedly. She's getting smarter, tho. She's carrying more weapons, practicing more with weapons, hiding more weapons and learning to use lock picks. And she's gotten really suspicious and generally taken to expecting if not the worst from people, at least anticipating that they might be up to no good.
The romance with the Stormdancer Kade continues. She graduates from the Keep. Most of the book is spent tracking down Warpers/users of blood magic. Interestingly, the climax involves _yet another_ grand development in Opal's powers, but rather than making her even more spectacularly unique, it has the effect of sort of negating a lot of things and simultaneously making her a lot like Valek from the Study series. Which is pretty weird.
I have no idea how far Snyder intends to go with this series, but there are some openings: the isolated community with the weird, skinny cult leader and the extremely powerful and sad young magician Quinn and his mysteriously symbol-ed collection of sea glass. Opal now has such substantial tactical, strategic and fighting skills that she'd be a damn fine agent in nearly any kind of nonsense. Add in the immunity to magic and the possibilities are probably endless. I like that she (apparently) can no longer make the magical glass messenger animals. Now that Sitia has had a taste of long distance communication and then had it taken away from them, I would expect them to put together a crash priority effort to create some analogous system.
Fun stuff. If you liked the Study series and didn't know the world continued in this series, I'd highly recommend giving it a shot. If you haven't read the Study series, I _think_ the two books would stand alone somewhat, but it might be confusing.