The author wrote that this was the most complicated thing she ever wrote, and I can definitely see why she said that. The book seems to be all over the place. In an effort to help you get the feel of this book I have written the review in no particular order.
While trying to make a synopsis for this book I'm still struggling. It's basically about a prison break, but in a world that makes no sense. I was confused for the first third of the book, and after that I was just waiting for something exciting to happen, but it never did.
Then there was this guy who was the prince, but he's not the prince, but the girl thinks he's the prince, but then he thinks he is the prince, but maybe he's not the prince, but then the people who should know don't know.
An ancient guy escaped from Incarceron, and somehow left clues that some unexplained professors have access to. And the professors are on both the inside and outside, even though nobody can escape. But maybe they created Incarceron.
The main guy inside had an oathbrother who was good, but then he acted shady, then he stole and murdered, then he acted loyal again, then he tried to get away from them. Then the slave girl, who swore a life debt to the main prince/non-prince guy, convinced the oathbrother to go back, so he did. But he's not what he seems either. Then she seems to fall in love with the prince/non-prince, or at least gets jealous, so she has some kind of thing for him, that is also never explained fully.
There is also this prince in the other world, who is a jerk. He's the late king's son with his second wife, so the son of the current queen, who is the second wife of the late king. She rules the kingdom, and to make her son, the jerk guy, the next king she did something to the king's older, and not so jerky son, which gives us the idea that he's possibly the prince in Incarceron, the prison, but that is never confirmed. By the way she's a sorceress with powers to stay young, but no other notable powers that we know of.
The girl who is betrothed to the jerk prince, but is seeking the non-jerk prince and is the daughter of the warden of Incarceron, but not really the daughter of the warden, and she's kinda interested in her teacher who is one of those unexplained professor types, and he is a master of all kinds of super advanced technology, which is outlawed for some unexplained reason so people can live in a world that is like the regency era. Why?
There is also this old guy, who is the professor type person inside Incarceron, who names the prince/non-prince a starfinder or starseeker, or starseer (I don't remember) and that means something that is never fully explained, but basically he looks out for the boy because he thinks it will lead him to his eventual freedom from the prison.
Oh ya, and the prison is alive, and can pretty much kill everyone whenever it wants, but it doesn't, then they get the key (shown on the cover) which for some unknown and unexplained reason, makes them invisible to the prison, so it can't kill them, or even stop them from finding the girl who eventually come into Incarceron to get the boy/maybe-prince, and they leave.
At the end they make a bunch of promises that they don't keep and that will probably be answered in the sequel which, I imagine will answer all the unanswered questions and make me go... "Oh, well that all makes sense now." But for now I'm just confused.