I absolutely loved this book! I admit that at first it was the cover that attracted me, because it looks so cool, but it was the summary description that pulled me in. 
 Let me just say that the whole book was nothing like how I expected it to be: I was under the impression that Blaire was already going to have the powers mentioned and we would get a look at her going through mirrors in the beginning and her explaining that she had the ability for a while and telling us about it but instead I end up confused and wondering what book I'm reading. I swear I had to make sure I was reading the correct book because it seemed like it was mostly about her father's disappearance and trying to figure out what happened to him, at least in the beginning. Then it started to get interesting when she actually did start breaking symmetry (walking through mirrors) and we get to Damian, too. 
 But, I admit the things that befuddled me where the jargon used, (sometimes I was seriously confused about terms and I had to reread the explanations it had to do with breaking symmetry to fully understand) and also as to why the father would have given her so many advice on how to be sneaky, etc. (but after learning more about breaking symmetry, I realized that it had to do with crossing over.) The characters, the premise, and just the whole book was awesome. It had elements of action, and just enough mystery/suspense that kept me on edge wondering what was going to happen (view spoiler)[like why the artifact had Blaire's DNA in the first place (hide spoiler)] and who exactly was the bad guy in the story ('cause c'mon, there's always a bad guy). The world building and idea was well done, although it could have been interpreted as any city in any country. (view spoiler)[The world building was done exceptionally well to explain the whole crossing over thing, but I would have liked more insight on the whole crossover sickness and what exactly came back possessing Amy when she succumbed to crossover sickness (hide spoiler)] 
 One of the things I loved was how sassy and sarcastic Blaire was (I could totally relate to her on that account seeing as how I would have said the same thing). Plus not to mention the "romance" between them was believable, to a certain extent (you'd understand if you've read it) but without spoiling anything, let me just say that the ending was sweet. And speaking of the ending, that was totally unexpected, although there might have been more than enough clues spread over the book it didn't quite click until we figured out what the artifact in fact was. Seeing as how some things happened in one of the deeper levels (view spoiler)[a certain character's death (hide spoiler)] I didn't really think that Blaire was going to end up with a happy ending after all but I was surprised when she managed to get to the real source and she did have a happily ever after. 
 Through the complexities and the heartbreak, plus the frustrations at certain parts, this is definitely one of my favorite books and one of the best I've read in a while.