The story is set in a doomsday world where most humans have died. The mutated cold-blooded animals dominate the power of life and death in this world. The remaining humans are forced to move into underground bunkers in order to survive, living in fear all day long. Joey (Dylan O'Brien) separated from his girlfriend Amy (Jessica Henwick) in the disaster seven years ago. Now they are in two different bunkers, relying on radio communication. One day, Joey, who missed Amy very much, decided to step out of the safe zone and return to the world above. He walked alone to the camp where Amy was. Along the way, he encountered countless dangers, and also met his mentor and friend Clyde (Michael Rooker) and Mino (Ariana Greenblatt). Can the cowardly Joey live to see Amy?