3.5 stars!!! 
 A nice and enjoyable YA sci-fi read. The story was fast paced and kept my interest till the end. The worldbuidling was okay but nothing to rave about. Enough was described to get a rough picture of the different worlds. I liked the idea of parallel universes with different versions of Earth and the ability to travel between them. There's also mention of humans with enhanced abilities and the science involving the multiverse which I found to be interesting. Estele's character was enjoyable. She came across as a well rounded person and I found her ability to handle difficult situations quite refreshing. There is a romantic element but the story doesn't revolve entirely around it. However, I have to admit that it came across as very insta-romance as at the beginning Stel seemed to prefer Flinn and then the next 5 minutes, she has all these feelings for his brother Cohl? I would have liked a bit of build-up to it or an exploration of their feelings towards each other. But, I did like their interactions with one another. 
 I loved the family dynamics throughout the book. There is a fair amount of action, conspiracy and betrayal also thrown in. Overall, I would say it's a great start to the series and I can't wait to read what comes next.