The movie starts off with a woman in labor being observed by Papa Hades (
Michael Bailey Smith). Papa Hades pulls the baby from the mother and watches it die. A few seconds later, he kills the woman.
A group of scientists are stalked and killed by the mutants while exploring the mining community.
Nearby, U.S. National Guard members are training on a replica of the streets of
Kandahar. On their way home, they drop by the area where the scientists were and start a rescue mission after they hear groans on their radio and notice a reflection in the hills. Sarge tells Napoleon to mind the porta-pottie, because of his complaining that they should alert base that they are going on a rescue mission, but Sarge doesn't listen and they continue to leave for rescue mission. Sarge tells Amber to stay behind with Napoleon and try make contact with the people in distress. Napoleon uses the Porta-Pottie. While using it a hand comes up the toilet, Napoleon runs out of it. He gets Amber to look in it then the body of the scientist climbs out, the scientist has been stuffed down the toilet: he is dying of severe infection after being cut all over and then immersed in feces. Napoleon and Amber ask who has done this to him; he replies 'They're Here' and then dies. Amber says it's a good idea to go catch up to the others so they will be all together but Napoleon stays behind trying to make contact with Sarge by radio.
Amber (
Jessica Stroup) is then attacked by a mutant; he is shot by Nikki (
Reshad Strik), and flees into a hole in the ground that leads to the mines below. Moments later, another mutant seizes Nikki and drags him through a tiny hole in the cliff face ripping his legs in half whilst doing so Amber could not pull him out.
Spitter (Eric Edelstein) is attacked by one of the mutants jumping on him, and while shooting, he accidentally kills Sarge (
Flex Alexander). Spitter dies after the mutants cut the rope he is using to climb down the cliffs while carrying Sarge's body.
The guardspeople then meet an injured Redding who explains what the group are dealing with and commits suicide. After, Amber and Missy (
Daniella Alonso) draw out one of the attackers, and Stump (Ben Crowley), Delmar (
Lee Thompson Young) and Crank (
Jacob Vargas) shoot him dead.
Missy is captured by Chameleon (Derek Mears), and the group follow her, with the exception of Stump, who decides to climb down the cliffs. As he passes a cave opening, Letch (Jason Oettle) slices off his arm and Stump falls to his death.
Chameleon plans to rape Missy and starts licking her face with his long tongue, Missy bites his tongue off and kicks him away, but Papa Hades comes in and throws Missy to one side and starts hitting Chameleon and Chameleon flees, Papa Hades pins Missy down with drool hanging from his mouth and starts raping her. Chameleon then encounters Amber and Napoleon in the mine and they kill him in a brutal manner.
Delmar and Crank come across Chameleon as does Grabber (Gáspár Szabó). Grabber opens fire with one of the group's stolen
carbines, and in the exchange Delmar is wounded and Grabber is killed.
They meet up with Amber and Napoleon, who then encounter Hansel, who is willing to lead them to where Missy is being held. They come across a room full of mutilated bodies, where Delmar collapses and dies. Crank discovers some dynamite and is killed by a
booby trap.
Amber and Napoleon come across a room populated by mannequins, and are attacked by Letch, who they kill. They come across Missy, who is tied down and being raped by Hades. Amber uses Missy's cell phone to distract Hades. After they untie her, Hades bursts through a wall. Amber uses her last
round to shoot Hades in the head. Napoleon shoves a spear into Hades and Amber pushes her fingers into his brain through the bullet hole, causing Hades to collapse. Missy, Amber and Napoleon finish Hades off and leave the mine.
As they leave, they were being watched by an unknown person through a computer with
infrared sensor on a laptop computer, which is shut by an unseen person who is wearing a tattered glove similar to those worn by some of the mutants.