An adventure-loving couple convince their friends to explore a remote, uncharted cave system in the forests of Northern Australia. With a tropical storm approaching, they abseil into the mouth of the cave, but when the caves start to flood, tensions rise as oxygen levels fall and the friends find themselves trapped. Unknown to them, the storm has also brought in a pack of dangerous and hungry crocodiles.

Seven years after the Monsterpocalypse, Joel Dawson, along with the rest of humanity, has been living underground ever since giant creatures took control of the land. After reconnecting over radio with his high school girlfriend Aimee, who is now 80 miles away at a coastal colony, Joel begins to fall for her again. As Joel realizes that there’s nothing left for him underground, he decides against all logic to venture out to Aimee, despite all the dangerous monsters that stand in his way.