Incarceron is a Science Fiction (with the feel of, and marketed as Fantasy) duology by Catherine Fisher. It tells the story of the prison complex known as Incarceron. Incarceron is infinite, inescapable, and to top it off, it's a malevolent sentient being hell-bent on forever confining the thousands of inmates inside it. No one enters, no one escapes — except one boy. Finn is a troubled inmate with vague memories of another life outside the prison.During a struggle within the prison, Finn finds a crystal key, which he and many others believe may be the key to Incarceron. He soon discovers that the key has another purpose; through the key, which turns out to function as a communication device, he meets a girl named Claudia. Claudia claims to live Outside Incarceron, but is doomed to an arranged marriage. With help from Claudia and from visions of the legendary Sapphique, Finn is determined to unlock the mysteries of his past and perhaps escape from Incarceron.The sequel and conclusion, Sapphique, reveals greater problems now that Finn has Escaped and is challenged as crown prince by a remarkably similar boy.
Bigger Bad: While Queen Sia is the main threat in the Realm, the true evil is Incarceron.
Bittersweet Ending: Incarceron is calmed and the masquerade has been broken, but some characters are dead and the people's way of life is reduced to medieval peasantry.
Chain-gangs also qualify, being a group of people fused together and sharing a consciousness. They assimilate their victims.
Briar Patching: One of the tales of Sapphique involves him facing off against a giant mechanical wolf that threatens him with many deadly fates, but Sapphique begs above all else, not to be thrown into the lake. Of course, when he is thrown into the lake, he swims to safety.
Chess Motifs: Barely noticeable in the first book, but emphasized more in Sapphique.
Crystal Dragon Jesus: Sapphique, the only known escapee, is worshiped as a god, known only as "The Nine-Fingered One" to his followers. He gained this nickname as the result of losing one of his fingers to a beast within the Prison.
Gilded Cage: It may be open Outside of Incarceron, and the nobility may have a high standard of life, but people are still forced to live as if they were still in a medieval period.
Good Is Not Nice: Keiro is a callous Combat Pragmatist that everyone but Finn seems to assume will betray them the second it's convenient for him, but he honors his bond with Finn and saves him and Attia several times throughout the books.
Grand Theft Me: A heroic example; Jared puts on Sapphique's glove and enters the body Incarceron was trying to use.
Had to Come to Prison to Be a Crook: Before he was put into Incarceron, Finn was a gentle prince. His time in Incarceron changed him a lot, as lampshaded by many.
Handicapped Badass: Jared's sickness tacks an "invalid" label on him that most everyone agrees upon. It doesn't make him any less of a badass.
It Was With You All Along: Claudia had been looking for an entrance to the Prison behind the gate, but found nothing. Only later is it revealed that the Warden keeps it as a charm on his watch.
Jerk with a Heart of Gold: Keiro, Finn's oathbrother, can be quite rude, and sometimes even mean, but that doesn't stop him from being a good friend.
Laser-Guided Amnesia: Finn. He can't remember his childhood, but recalls vague bits from his past.
Slap-Slap-Kiss: Keiro and Attia have this dynamic, though romance is debatable.
Split Personality Merge: While they were originally separate, at the end Jared's gentle personality is placed within Incarceron's, calming him.
Super Intelligent: The Sapients, who created Incarceron and now hold all the advanced knowledge of the past before Era.
The Stoic: Playing the nobility game Outside means being this all the time. Queen Sia and the Warden are unmatched in this respect.
The Wall Around the World: Near the end of the first book, Finn and gang fly a silver airship into the hole of what seems to be this. Whether or not it actually was is debatable.
Tough Love: Although John Arlex is hard on Claudia and has essentially raised her to become the perfect Queen, he eventually admits that he grew to love her as a true daughter.
The Unmasqued World: At the end of Sapphique, the holograms and everything that kept the nobility in power are broken, and the people can see what the world really looks like.
Weather Control Machine: Incarceron controls its own climate, able to make the temperature unbearably hot or freezing cold.
What Could Possibly Go Wrong?: Let's face it, a sentient prison is not a good idea. Especially if there is no way out whatsoever.
You Are What You Hate: Keiro hates the Half-Men, people with mechanical limbs that were either born with them or "fixed" by Incarceron. It later turns out that Keiro himself is a Half-Man, and one of the reasons he hates them so much is because he was born with it and he's not sure how far the mechanical parts go.