The world has changed. The only habitable place left for humanity is in the high mountains, above 8000 feet. Below 8000 feet dwell the creatures that killed 95% of the human population less than three years ago. To save the life of his young son, a father (Anthony Mackie) is forced to venture below "The Line" with a scientist (Morena Baccarin) he despises, but who just might hold the key to defeating the monsters, and a young woman (Maddie Hasson) determined to keep them both alive long enough to save the human race.