Spell Bound takes off immediately where Waking the Witch left off, with Savannah's powers gone. After regretting how the last case ended, she had made a wish that she would gladly give up her spells if only she could fix some of the problems her investigation caused. As it turns out, someone took her up on her offer. Having already finished the concluding trilogy of the series, I will say that this one does kind of fill like a middle book. Waking the Witch introduces Savannah as a narrator and begins some of the plot lines that will run through the rest of the series, while Thirteen wraps them all up. Spell Bound, in comparison, definitely feels like it's getting things into place. Since it is Armstrong, it is a very action packed getting things into place, but the central mystery/story isn't that memorable compared to the other two of the trilogy.
Basically, it turns out there is a group of supernaturals that want to expose themselves to humans, and possibly even rule over them. This impending war has lots of people taking sides - most of the knowledegeable supernaturals, such as the Cabals and the Council know that it is not worth the risks, but some supernaturals that aren't as involved and are more on the outskirts are tired of hiding. Even the afterworld is seeing chaos, and demons are taking sides - Savannah's demon grandfather and Adam's demon father are on opposite sides of the dispute. While this supernatural exposure threat is looming, Savannah doesn't have her powers and she has discovered that the witch hunters are not a fairy tale after all, having become the target of one during her last case. Much of the novel involves these three threads, and how Savannah faces the fact that she has relied overly much on her powers without doing the proper work. Given the threat, basically all the other characters from previous novels are called in and appear at one point or another, including Savannah's brother Bryce who ends up being a key part of this novel. Even Eve and Kristof Nast show up through communications with Jaime Vegas.
Overall, I think it was a fun ride like most of Armstrong's novels but I also think this one wouldn't have stood as well on its own, without me having the follow up novel on hand. In general when I read a series, I try to make myself review one before I read the next but since Armstrong switches up the narrators, I haven't followed that rule as closely with her novels. There was much less danger of the lines blurring as far as what occured in which book given that they all had distinct stories and different main characters. This is definitely not the case with these last three because they all have the same narrator, there is so much going on, and the last three novels take place over the course of a week or so.