I don't really buy the whole your soul mate is the kind of person you don't want thing. In the first book I believed it, since Casey was a half human and Theron hated that, but I don't see how Callia was that for Zander. He does think at one point that he should have known better, since she's his soul mate. His assumption is based on something that isn't really true (kind of important to the plot, so I won't give it away). They'd been lovers ten years before and were torn apart by lies that other people told. They both spent a lot of time denying to themselves that they still feel anything for the other. Nobody believes you, if you've got to spend that much time convincing yourself of it you aren't going to be able to convince anyone else.
Most of the things I can think to say about the plot are spoilers, so I'll just say that there were some twists I didn't expect and at least one I did.
I'm really glad that the next book is Isadora's since this book makes the second time one of her almost husbands has found their soul mate. I was afraid it was really going to become a pattern.