There might be some minor spoilers below, I'm not sure what you'd consider a spoiler, but no large plot twists revealed anyway. So read on my friends :) if you wish 
 Incarceron was a very different book to other's I've read. I thought the idea of a living prison was very unique and intriguing, especially when thrown in with the espionage and deceit of Claudia's palace life. At first glance Claudia and Finn's lives seem extremely different, but looking more closely, both worlds are similar in the evils surviving there. While the Outside is definately a better place to live, you can never know who to trust, while certain things are also forbidden and spied on. 
 A few things I didn't like about this book though, would have to be the pace. Sometimes events seemed to drag on longer than neccesary, and it also took far too long for Claudia and Finn to have any sort of encounter. 
 Now the characters... 
 In my opinion some of the characters seemed kind of flat with only minor ways to be able to establish differences. I think this applies to Finn the most, because although I liked Finn, I just don't feel as though I know him as well as some of the other secondary characters who didn't even narrate, such as Kiero or Jared. Claudia also, I don't know her very well still, and I must admit that what I do know, I'm not all that fond of. She seems nice enough, but it seems that growing up in that deceit filled castle environment has messed with her head a bit, filling her with too much caution and self gratification. Jared, her mentor, I did happen to like very much though. He seemed to be out for everyone's best interest. I don't know, my thoughts might be somewhat in his favor because I always seem to like the sick people. 
 brief review of secondary characters: 
 The Maestra: nice sometimes, otherwise, bitch 
 Attia: Idk, she might be trouble, I'd keep my eyes on her 
 Gildas: selfish asshole 
 Kiero: kinda violent and selfish, but I actually like him 
 Warden: he could be nice, Idk, I think Claudia's view of him might be slightly flawed 
 Queen: bitch 
 Casper: He seems fine to me, idk why Claudia hates him so much. He gave her permission to cheat on him, sounds like an okay marriage to me if it must happen. Because, of course, if I was marrying him, I'd cheat. He's an ass, but an idiot. She would rule that marriage. 
 I know it seems like I didn't like this book very much, but I actually did, and I'd recommend it. :)