The Scorch Trials (The Maze Runner #2) by James Dashner

Goodreads Synopsis
Solving the Maze was supposed to be the end. 
 
Thomas was sure that escape from the Maze would mean freedom for him and the Gladers. But WICKED isn’t done yet. Phase Two has just begun. The Scorch. 
 
There are no rules. There is no help. You either make it or you die.
 
The Gladers have two weeks to cross through the Scorch—the most burned-out section of the world. And WICKED has made sure to adjust the variables and stack the odds against them. 
 
Friendships will be tested. Loyalties will be broken. All bets are off. 
 
There are others now. Their survival depends on the Gladers’ destruction—and they’re determined to survive.