Young teenager Jack Sullivan and a group of friends live in a decked-out tree house, playing video games, eating candy, and fighting zombies in the aftermath of a monster apocalypse.

It's been several months since a mysterious portal opened up in the sky, spawning various monsters and zombies, and thus effectively dooming the human civilization. With all the adults and cool kids either zombified or evacuated to unknown safe zones by the remnants of the Military, teenager Jack Sullivan finds himself no longer the awkward, ignored kid he once was in his abandoned hometown. He and his surviving friends are determined to survive the apocalypse in style as the apex predators of this brave new world, made difficult by guests from the other side, rampant monsters, and the endless zombie horde.