The Kill Order (Maze Runner, Book Four; Origin): Book Four; Origin

Before WICKED was formed, before the Glade was built, before Thomas entered the Maze, sun flares hit the earth, killing most of the population. "The worst is yet to come." Mark and Trina were there when it happened. They survived. But now a virus is spreading. A virus that fills humans with murderous rage. "There is no cure. No escape. " They're convinced that there's a way to save those who are left--"if" they can stay alive. Because in this new, devastated world, every life has a price. And to some you're worth more dead than alive. "The end is only the beginning."