A mysterious green gas released upon the world causes the earth's entire plant life to slowly wilt over and die. Oxygen levels drop to dangerously low readings bringing forth the birth of strange new technologies and surgical procedures to combat against the effects of the poison air. Flash forward ten years to the story of a group of survivors as they struggle to find salvation in the desolate world. With oxygen now completely non-existent in the air, their existence relies upon a strange machine to provide them with the clean air they need. After years of isolation, they encounter what appear to be other humans outside in the oxygen-deprived atmosphere. Uniting with their new friends and now hopeful, they embark on a mission to find more survivors. But the path ahead holds many dangers and one person in the group has been hiding a dark secret from them.