** spoiler alert ** 
 I liked it well enough, It was fast paced full of action and we get to know the other characters better (number nine is awesome). 
 It was really good, but for Sarah... I mean, I was so happy last book, I thought she would be out of the picture after the betrayal, but suddenly she shows up at the prison and all is well? They didn't even explain the messages she she sent, and why she was acting weird when Four got caught!