Tl;Dr: If you thought Marguerite and Paul had problems in the first book, just wait til you seen what's in store for them in this one. Ten Thousand Skies Above You is an emotional roller coaster with an ending that leaves you hanging from a cliff so high you can't see the water. 
 I've been pretty excited about this book since I read A Thousand Pieces of You this time last year, and I am very happy to say it does not disappoint. The first chapter or two are a bit meh- mostly just a lot of recap from the first book that I think it could have done without. But once the book got going, I couldn't stop turning pages. 
 Some of you might remember that I had wanted the last book to delve into the ethics of the firebird project a bit more, especially considering Marguerite's actions in the Russiaverse. I was hoping that this book would address the grey areas a bit more. Fortunately, in some ways, the question of the ethics of taking over an alternate version of yourself's body was central to this book. Not only is Marguerite forced to question her present actions, but also to grapple with the consequences of the decisions she made in the universes she visited in the first book. I don't want to go into specifics because spoilers, but I was really happy with how this book handled the ethics questions and it definitely sets it up for the next book to force the characters to grapple with them even more. This is one of the more interesting aspects of the premise of these series, in my opinion, so I look forward to seeing how the characters react to everything that has happened. 
 Marguerite and Paul's ship is still sailing, but it definitely hits some rough waters in this book. What I like best about the conflicts in their relationship, though, is that it is not the usual petty stuff we so often see in YA (YA writers I love you, but you know its true). The complications in their relationship stem directly from their experiences with their alternative selves. Marguerite struggles to separate the actions of one Paul from the other, and their ideas about a shared destiny across every universe is strained as Marguerite encounters some universes very different from their home world. As a result, the conflict is both realistic and interesting, as opposed to just being frustrating an annoying (see: The Selection Series). 
 All in all this second book in the Firebird series builds upon the first one really well. As always it was exciting to see where Marguerite ended up after every jump, and what sort of trouble she would get herself into. And by the end we learn that the Triad conspiracy goes much deeper and much darker than we ever could have expected after book one. Prepare yourself to be frustrated after the last page- you're going to desperately wish you had one more left to turn!