We will get control of the earth again because failure is not an option.
Demons have completely overrun earth. They are culling humans, burning down cities and making it literally Hell on earth. Teagan and the hybrids struggle to save as much of the human race, while waging a war against the demons.
As if that isn't enough, a new enemy enters the scene. What makes a demon scared? You never want to find out. Humans are about to discover that there are worst things lurking in Hell than demons. When the demons escaped so did the Nameless.
With the arrival of this new enemy, demons and humans enter into an unlikely and temporary truce to battle this foe. Even their combined power and strength might not be enough to defeat this terror.
If they can't drive back the Nameless, it will be annihilation of demons, humans and anything living in earth.