Sarah Tyler (Isabella Calthorpe) is driving along a winding road one night in order to return to her home in England. after a couple of years of staying in the Los Angeles in the United States. When she arrives, she greets her step-father who is working his way through a couple of paperworks. Sarah told her step-father to rest that night while she takes care of her brothers who are at the barn fixing a jeep. Sarah left the house to go to the family's barn nearby while a storm is brewing. She saw her brothers with their friends having a party at the barn. Among those partying were Stephen Moore (Peter Gadiot) and his girlfriend Emily (Gemma Atkinson), Charlie Moore (Gabriel Thomson), Gary Ashby (Tom Felton), and Doug Walker (Joshua Bowman). Also in the barn away from the noise of the party is their youngest brother Luke Moore (Anthony de Liseo) asleep amongst the hay together with their dog Stoner.
Sarah woke up Luke and learned that their parents were fighting over bills and a supposed love affair of their mother with another man. She told Luke to go back to sleep and sent Stoner back home. Sarah then joined the party where she asked why she was kept out of the loop for so long. Stephen then told her that her step father accused their mother of having an affair with someone and that she is paying this man huge sums of money. Sarah can't believe that her mother is having an affair.
Everyone went back to the house. There was a power outage caused by the storm. Inside, the pack went up the stairs and noticed blood dripping at the top of the stairs. Meanwhile, Gary separates from the group and ended up in the kitchen in order to look for candles. The group upstairs followed the marks of blood on the carpet and they saw that it came from their father's room. When they entered the room, everyone was shocked to see the lifeless body of their father that seemed to have been attacked by some wild animal. The rib cage can clearly be seen with some internal organs missing. Almost at the same time, Gary saw some candles and dropped them. When he reached down to get them, he saw the collar of Stoner and the bloody remains of the dog.
The group upstairs suddenly saw a beast like creature which immediately attacked them. Luckily, they were able to close the door before the beast could reach them. The beast keeps on pounding furiously against the closed door when Gary called out to them. The beast immediately heard Gary and went after him and killed him the same way - ripping his internal organs out. The creature then started to go back to the closed door and furiously tried to break it open. Sarah and group then fled to the bathroom of their father's room and closed the door there. When the beast started to pound the door of the bathroom also, Sarah saw a passageway inside the bathroom going to the attic. Everyone went up it and for a moment in time they were saved.
In the attic, the group contemplated on what they are going to do. Sarah mentioned that they needed to get help and her mobile phone is in her bag downstairs. Stephen's phone is dead. Sarah remembered Luke was left sleeping at the barn. Sarah then said that there is a phone in their father's room. Emily saw a pathway in the attic that leads to another opening in another room. They devised a plan in order to get to the phone. Sarah would go down through the other pathway and make distract the beast while Charlie goes down to their father's bathroom back into their father's room and use the phone there to call for help.
The monster heard Sarah's screams to get it's attention and ran towards her. Meanwhile, Charlie was able to reach the phone and he tried calling the police. Sarah went back to the other opening in the attic when she noticed that the creature had stopped following her. She went outside to look for the creature and realized that it is after Charlie. Charlie was able to contact the police and mentioned about the wild animal in their house before he was attacked and killed by the beast. Sarah saw that Charlie was already being devoured by the beast. It then went after Sarah, who immediately tried to go back up the attic. Unfortunately, the beast was able to get hold and bite her leg before she managed to make her way up to the attic.
On the other side of town, McRae was picked up by police officer May. Apparently they were sent to investigate the call made by Charlie about wild animals being loose at their home. McRae is a trained dog catcher and was enlisted by the police department to help in resolving the situation. May thinks that the report is a hoax but went there instead to be sure.
Back in the attic, Stephen was hysterical while Doug was treating Sarah's leg lacerations. Stephen crawled in the attic away from Sarah and Doug while Emily followed him. Stephen saw another passageway from the attic which lead to another room containing a shotgun. Once inside the room, Sarah and Doug warned them that the beast is lurking outside the room and told them to get out. Emily and Stephen manage to block the door after a little bit of struggle. While Emily is looking for shotgun cartridges, Stephen leaves her and crawls back up to the attic. Sarah armed with a stake makes her way down where she injures the beast before it attacks Emily.
All of them meet up at the attic where an outraged Emily starts screaming and threatening a scared Stephen. She takes the shotgun and says she will kill the beast herself. The beast manages to surprise Emily where she takes a shot at it but unfortunalety falls and ends up shooting herself which results in her death. Meanwhile, McRae with officer May see an abandoned car in the middle of the road and stop to investigate. They come to the conclusion, after finding that the woman did not take her handbag, that the car broke down but the driver seeking for help never made it back so the call they received earlier may not be a hoax. As they leave, a pile of clothes is shown a few feet away from the car.
Luke wakes up and goes back to the house unaware of the situation that is going on. He finds Gary's dead body in the hall way. The beast, now aware of his presence, is after him. Sarah eventually falls through the ceiling. As she quickly recovers she helps Luke and all of the remaining survivors make their way to the roof. McRae and officer May arrive at the house but both get killed by the beast. Sarah manages to reach the police vehicle where she takes the handbag and then all of them run towards the barn where Stephen tries to fix the Jeep. Sarah discovers that the handbag belonged to her mother, it is also revealed that Stephen tampered with his mother's car so that he can delay her from seeing her lover. Sarah says that if their mother is dead then Stephen is the one to blame. An upset Stephen knocks her unconscious but Sarah awakens and hits Stephen. A scared Stephen runs out of the barn and he is attacked by the beast. Inside the barn Sarah starts to transforms into a monstrous figure.
Luke and Doug run back to the house where the beast comes back. They hide under the table and just as soon as the beast is about to kill them, a beast-like Sarah attacks and fights with the other beast. Luke runs back to the car while Doug tries to shoot at the beast but is eventually bitten and killed by Sarah. In the morning Sarah has returned to her human self. The other beast is revealed to be Sarah's mother. Sarah finds Luke inside the car and they both drive off to go somewhere safe. Just before the credits roll, it is revealed that Gary is still alive.