Ten years ago, the world ended. Fifteen-year-old Mia lives with her mother in an underground colony, where they have food, shelter, and protection from the ravenous creatures that roam the planet. Life in the colony is perfect...except for a law that states that all women from ages sixteen to fifty must give birth to as many children as possible to help repopulate the earth. And Mia's about to turn sixteen. Mia's mother doesn't want that kind of life for her, so she convinces Mia to escape, disguised as a boy, and embark on a treacherous journey to meet up with her cousin Caleb. Mia's guide is a mysterious traveler named Derek, and together, they must fight their way across the frozen wasteland and discover, despite the horrors necessary for survival, what type of people they truly want to be.