The film opens with four people running from an unseen creature. One of them (Eve) is caught and mauled to death, much to her husband's horror. They race off as the creature begins to consume her.
Some time later, a group of five friends, consisting of Jeff (Parker Young), his step-sister Alissa (Keke Palmer), her best friend and Jeff's girlfriend Mandy (Elizabeth Gillies), Alissa's boyfriend Matt (Jeremy Sumpter), and Jeff's friend Sean (Paul Iacono), enter the woods for a camping trip, only to find the trail blocked off for forest rejuvenation. Undeterred, they park their car and go hiking. Matt finds a Marine's discarded backpack. Later that night, while the others discuss which way to go, Mandy walks off the trail to see bits of human remains and screams. The others rush to her side and upon discovering what she saw, decide to call the rangers once they get back to the car. On the way there they discover an mutant creature feeding on a upon something unseen. They attempt to go around it at first but it hears them and looks towards them. Jeff tries to scare it off only for it to become aggressive and chase them down. While hiding out they find the abandoned house from earlier in the movie. Jeff decides to distract the creature while the others run to the house. Unfortunately, he did not know that it was behind him and it attacks and kills him as the others run to the house, horrified at Jeff's demise, and plead to be let in. One of the men inside the house opens the entry way and lets them in. As they run in, the creature grabs Mandy and begins to pull her back while a woman lights something on fire and throws it at the creature. It lets go and they pull Mandy inside the house and the woman tends to her wounds.
They meet the three survivors from earlier, Carl (Thorsten Kaye), his wife Vicky (Joey Lauren Adams), and Douglas (Amaury Nolasco), who have been hiding from the monster inside the house and barricaded every door and window. They explain that the house was abandoned when they got there but they did not put up all the barricades. The group decides to help them barricade the house some more and strengthen the weak spots as the creature apparently tests for weak spots and seems to know something about the house as it earlier at an unseen point broke in through the cellar. Douglas refuses to help and remains upstairs. Alissa attempts to rationalize this in the kitchen while Matt tells her she's over thinking this and that it is just an animal. The creature attempts to break in through the kitchen window and Carl and Sean rush in and helps them barricade the window with a door. The creature then begins to test for weak spots and crashes in upstairs. While Douglas comes downstairs because of this, Carl, Sean, and Matt go upstairs to find it while Vicky goes to get fire. The group upstairs discovers creature in a room and try to close the door while the creature tries to break it down. Downstairs, the stick won't light and Mandy and Alissa rush upstairs to help and struggle to put drag a dresser in front of the door. The creature breaks a spot in the door open as Sean rushes downstairs. The girls continue to struggle as Sean then returns with Bear Replant from earlier in the movie and sprays the creature in the face. It seems to work as the creature runs off and Douglas finally helps and helps put the dresser in front of the door and says it won't hold and that they need to get out of there.
Downstairs, they gather and while Sean remains hopeful that the help he contacted earlier will come, Douglas denies it saying he already tried earlier and no one has come. He says they need to sacrifice someone to get out and Carl disagrees refusing to kill anyone. Matt agrees with both and decides to go for help while Carl and Sean distract the monster while the four groups stay in contact with walkie-talkies, but it catches on and attacks Matt who warns them the creature is coming. Carl and Sean attempt to get back into the house but Douglas refuses them entry saying that they all heard Matt say the creature was coming. Vicky attempts to let them in but is knocked out by Douglas and Alissa contacts Carl and Sean, telling them to go to the kitchen door. The creature approaches and still Carl has not responded. The creature comes onto the porch just as Carl responds and sees that the flare and walkie it followed was abandoned by Carl and Sean who are now inside the house through the kitchen door. Carl knocks out Douglas.
Douglas wakes up tied to the stair well and demands to be let go. Alissa looks around the house as Mandy follows. Alissa says she wants to kill the monster for what it's done and Mandy hugs her sobbing and reveals that she is pregnant and to count her in on whatever she is planning. They go and find Sean who is in hysterics from all the stress and does not want to die with a secret. He reveals that he and Jeff were having an affair. Alissa breaks up the verbal argument that follows and the group hears beeping coming from a walkie in the living room. They find that Matt is paging them and is alive in the cellar. Carl leads Alissa and Mandy down and begins to help get Matt out of the cellar upon his discovery with Mandy's assistance. The creature is shown to be waiting and Carl sacrifices himself to give the others time to get Matt out.
Alissa attempts to keep Matt alive as the tied up Douglas, Mandy, and Sean look on. Vicky is elsewhere in the house sitting in shock and mourning her dead husband. Matt attempts to tell them something regarding the creature as Alissa continues to try and help him. Douglas tells her Matt is dying but she is adamant he can be saved. He continues to try and convince them that Matt is better off being used as bait for their escape as Vicky returns to the room. He asks for a better plan, expecting none, but Alissa says they know if they open the door the creature will come in and suggests trapping it and burning the house as they escape. Douglas agrees and Sean says they need to act fast for Matt's sake. Douglas says he will help carry Matt as that is Matt's only chance. Alissa signals Sean to untie Douglas and he does. Matt attempts to tell Alissa he loves her but is beaten to death by Douglas while the others look on and scream in horror. He argues with the others saying it was simple and that he did not kill anyone, merely sped up a clock that was already ticking.
As Douglas drags off Matt's body while continuing to yell at the others, the creature breaks in through door and Douglas is then attacked as the others watch in horror. While the monster devours Douglas, Alissa grabs matches and a bag and they retreat to the kitchen while Alissa goes to grab the kerosene she saw earlier while Mandy stands watch. They begin to pour kerosene in the kitchen and as they knock something over the creature is finally distracted enough from consuming Douglas' body and goes to investigate. While a small area burns the creature investigates the house, looking for the others. Sean, Mandy, and Vicky have retreated to the cellar after closing it back off and listen to the creature search for them. Alissa closes the creature in a room where she begins to burn it to death. The others start to head out of the cellar from its other entrance as Alissa turns away from the fire. Vicky sees Carl's body and goes to his side and beings talking to him as if still alive as Mandy tells her they need to go. Sean screams for them and screams as he is tossed down, attacked and dragged off as another creature calls out. Mandy pulls Vicky away from Carl and they run off. Mandy escapes outside only to turn around and see Vicky in the doorway begin to bleed from her stomach as she is attacked from behind by the second creature. Mandy looks on and screams as she sees its head as Vicky is dragged away. She runs off to Alissa. They run off as the creature chases them. Mandy falls and as Alissa tells her to get up and that she can, the creature catches up. It attacks Alissa as Mandy screams and looks on in horror. As Alissa finally dies and the creature begins to consume her, Mandy runs. She throws her over shirt to throw her scent and covers herself in dirt to cover the rest of her scent from the creature.
She manages to make it to their car and start it as the second creature breaks through the drivers side window, she climbs out the passenger side and runs around to the drivers side as the creature runs around the car to get to her. She reverses as it begins to climb over the car and throws it off. She runs it over twice and the drives away. A third monster steps out of the forest, going to the second creatures side and calls out.