Addie and Eva are two souls in one body. They were supposed to settle around 4 years old, 10 years at the very latest. Settle on which soul will stay and which soul will fade away. Settle on which soul is dominant and will get to live. Eva didn't want to give up on life. She fought as hard as she could. But by 12 years old Addie had to settle and hide Eva's existence or risk being sent away to doctors and experiments and possible death. Eva shouldn't be there and no one can know. Eva continues to watch but she can no longer take control. 
 The two people in one mind idea kind of reminded me of The Host by Stephanie Meyer. One girl has full control while the other is just observing with no control to speak or move. Just trapped inside. Sounds like a horrible life! The book is told in the POV of the non-dominant soul Eva. Eva helps remind Addie and they keep each other company. They try to sneak by in their illegal existence until they meet a new friend Hally/Lissa who is also hiding the fact that she is a hybrid. Her brother Devon/Ryan is another hybrid. They want to teach Eva how to take control again but it is not so easy and not so easily hidden. 
 The book was easy to follow considering the two people in one mind aspect. Eva always talks about everything as "ours" which takes a little getting used to. The idea of two people in one head had my mind reeling. I kept thinking what if Eva falls for Ryan, which is what I kind of felt happening, then does Addie have to fall for Devon? What if they both don't fall for the two guys in one body? What do they do during sexy times? LOL When one girl is in control and the other is just observing?! Freaky! A lot of the questions I had, sadly were not brought up until the very end. 
 The book had little romance and was a bit slow during the middle but the whole idea was so intriguing that I was still glued to the pages. It was just so sad to imagine having to lose a part of yourself. Think of growing up with another person and then having to let them fade away. The government claimed two souls fighting in one body causes chaos and war in other places around the world. I would assume if two souls was the way we were born that we would figure a way to make it work. I think we will get more into that knowledge in the next book. Can't wait to see what happens next with the hybrids! 
 -I'm sorry- Addie said. -I'm sorry. I'm sorry. I tried--- 
 -It's okay- I said, because what else was I supposed to say? She was Addie. She was the other half to me. She was more important than anyone. 
 -I just never thought- She covered our face with our hands, trying to muffle her tears. -I never thought--- 
 Never thought she'd have to watch, feel, as we kissed someone she didn't want to. That had been my private fear. 
 My burden. 
 I didn't know what to say. 
 As they talk to each other in the book it is in But goodreads is trying to italicize that so I'm using - -