Authors:

The kid who didn't go back when he should have and now goes back when he shouldn't. The kid called Zombie, who made a promise, and if he breaks that promise, the war is over - not the big war, but the war that matters, the one in the battlefield of his heart. Because promises matter. They matter now more than ever.

Rick Yancey (2013). “The 5th Wave”, p.278, Penguin
The kid who didn't go back when he should have and now goes back when he shouldn't. The kid called Zombie, who made a promise, and if he breaks that promise, the war is over - not the big war, but the war that matters,