If you could imagine the bastard child of The Demon King (with it's monarch struggles), Divergent (with its government imposed way of life), and Terminator (machines are taking over!!) with a little bit of the Danger Room from X-men thrown in (obviously the jail), this is what you'd get with this story. This is a terrible description though since this book came out before some of these others. Nevertheless, I actually kinda loved this book. And it's ironic that it can go on both my 'future sounds depressing' and 'old school' shelves. I think this is the first book I've read that can be both.
If you disregard some of the basic questions like what happens to the prisoners and bad people that come along after the prison is constructed or why people decide to live in a past time period just to placate a king, you'll find a unique and interesting story. I liked all of the characters, I was taken by surprise more than once and I just generally had a good time with it once I got into the story. I'll be checking out the next book, I'm interested to see what comes next.