When Thomas wakes up he realizes that something is very wrong. The sky is just a dull gray color—no sun, no sky, just what looks like a drab ceiling.
The other boys are in a panic, rightfully so. How could the sun just disappear? This is just further proof that the world they live in is fabricated.
Thomas slowly makes the connection between the gray sky and what the girl said about triggering the Ending.
Poor Chuck is mind-boggled by the whole thing.
Minho finds Thomas to start their day, and Chuck is surprised that they are still going to go out into the Maze. Minho points out that without their "sun" the plants and animals will soon cease to provide food for them, so the desperation to find an exit just got stepped up a notch.
Shortly after they enter the Maze they see a Griever. It's just sitting there like the "dead" one that attacked Alby.
While they are hiding behind a wall debating what to do, it disappears. They quickly chase after it, and follow it all the way to the Cliff where it really disappears into shadow.