The door swung open into darkness. Beyond it, a chamber. And in the center of the chamber, a pedestal. On the pedestal, a glass cylinder filled with a clear liquid—and inside it, a key. But the floor around the pedestal was not stone. It was soft. Organic. It pulsed.

The routine of the Glade is shattered almost immediately after Thomas’s arrival. The mysterious elevator (The Box) ascends again the very next day, bringing a teenage girl named Teresa. She arrives in a coma, clutching a note that reads: "She's the last one. Ever." Her arrival signals that the status quo is ending and the "End Game" has begun.

Thomas realizes that knowledge often brings more pain than ignorance.