Beneath heaven is hell. Beneath hell is Furnace. Furnace Penitentiary. The world's most secure prison for young offenders, buried a mile beneath the earth's surface. One way in, no way out. Once you're here, you're here until you die, and for most of the inmates that doesn't take long - not with the sadistic guards and the bloodthirsty gangs. Convicted of a murder he didn't commit, sentenced to life without parole, 'new fish' Alex Sawyer knows he has two choices: find a way out, or resign himself to a death behind bars, in the darkness at the bottom of the world.

Only in Furnace, death is the least of his worries. Soon Alex discovers that the prison is a place of pure evil, where creatures in gas masks stalk the corridors at night, where giants in black suits drag screaming inmates into the shadows, where deformed beasts can be heard howling from the blood drenched tunnels below. And behind everything is the mysterious, all-powerful warden, a man as cruel and as dangerous as the devil himself, whose unthinkable acts have consequences that stretch far beyond the walls of the prison.