The Death Cure (The Maze Runner #3) by James Dashner
Goodreads Synopsis
It’s the end of the line.

Will anyone survive?
What WICKED doesn’t know is that Thomas remembers far more than they think. And it’s enough to prove that he can’t believe a word of what they say.
The truth will be terrifying.
Thomas beat the Maze. He survived the Scorch. He’ll risk anything to save his friends. But the truth might be what ends it all.
The time for lies is over.