The Maze Runner by James Dashner

When the doors of the lift crank open the only thing Thomas remembers is his first name. But he's not alone. He's surrounded by boys who welcome him to the Glade a walled encampment at the centre of a bizarre and terrible stone maze. Like Thomas, the Gladers dont' know how or why they came to be there or what's happened to the world outside. All they know is that every morning whan the walls slide back they will risk everything even the Grievers; half-machine, half-animal horrors that patrol its corridors to try and find the way out.