Becky, a rebellious 13-year-old girl, is still grieving over the loss of her mother. Her father, Jeff, decides to take her and his new girlfriend, Kayla, to their lake house for the weekend to bond with Becky and to announce their engagement. Unfortunately, their peaceful weekend is disrupted when a group of violent convicts led by Dominick, a white supremacist, breaks out of prison and arrives at the lake house searching for a mysterious key.
As the convicts take Jeff and Kayla hostage, Becky manages to escape and hides inside the house. She soon realizes that Dominick and his crew are not only looking for the key but are also willing to kill anyone who stands in their way. With her survival instinct kicking in, Becky turns from a naive teenager into a fierce and resourceful warrior, using her wits and her surroundings to take down the convicts one by one.
As the body count rises, Becky confronts Dominick, who reveals that the key unlocks a secret safe containing a lethal virus that he plans to unleash on the world. In a climactic battle, Becky manages to outsmart the convicts and takes vengeance on Dominick for killing her dog. The movie ends with Becky and her father reconciling, but Becky's traumatizing experience leaves her scarred and forever changed.