At a Texas high school, Mandy Lane (Amber Heard
) is a popular outsider. Fellow student, Dylan, (Adam Powell
) invites her to a party at his house and she accepts with the provision that her best friend Emmet (Michael Welch
) can attend also. At the party, Dylan and Emmet clash so Emmet goes to sit on the roof overlooking the pool watching Mandy. Dylan joins him and Emmet convinces him to jump from the roof to the pool to get Mandy's attention. Dylan jumps but misses, hitting his head on the edge of the pool and dies.
Nine months later, Red (Aaron Himelstein
) is having a party at his father's ranch and has invited Mandy along. She obtains permission from her Aunt (Peyton Hayslip
) and agrees to go. Following from Dylan's death she now refuses to talk to Emmet. On the way to the ranch, the kids steal a keg from a driver (Robert Earl Keen
) at a truck stop. When they arrive at the ranch Chloe (Whitney Able
) won't drive her car over the cattle grid and so with a shortage of seats Mandy and Bird (Edwin Hodge
) elect to walk to the ranch.
While walking they are picked up by Garth (Anson Mount
), the ranch hand. Once at the house they begin drinking and playing games. Mandy is the only one to stay sober. After a disparaging remark, Jake (Luke Grimes
) walks out, followed by his girlfriend Marlin (Melissa Price
). They stop in a cattle shed and, after engaging in oral sex, Jake leaves. Marlin is caught by a stranger and has her jaw broken by a shotgun. While looking for Marlin, Jake discovers her body and is shot by the stranger.
Bird, Mandy, Red and Chloe are joined by Garth at the house after a stranger in Red's car fires fireworks at them on the porch. Bird chases the car, believing that Jake is the driver, but he encounters Emmet. During their fight, Emmet blinds Bird by cutting his eyes, chases him and finally stabs him to death. At the ranch, Garth stays over. Mandy falls asleep in the kitchen. Red and Chloe fall asleep on the couch.
In the morning as they prepare to leave, Emmet shoots Garth. Red and Chloe escape out the back and run to Chloe's car. On the way they both encounter the bodies of Jake and Marlin. They reach the car and Red is shot as they kiss and, as she runs back to the ranch, Chloe finds the body of Bird. She is chased by Emmet in Red's car who has taken the keys from a dying Red. Meanwhile, Mandy retrieves the keys to Garth's jeep, and the hunting knife Emmet used to kill Bird. She then sees Chloe running towards the ranch, pursued by Emmet. As Chloe runs up to Mandy, she stabs Chloe in the stomach. While Chloe bleeds out, Emmet and Mandy discuss their plan.
Emmet has kept a journal giving the reason behind the killings since he and Mandy have previously agreed to a suicide pact. However Mandy refuses to take the pills Emmet gives her. They fight. Garth shoots Emmet who then attacks Garth with a machete. A brief chase ensues and after Mandy falls into a pit of dead animals, Emmet jumps on top of her. They fight until Mandy manages to club him to death with a log. Mandy then returns to a wounded Garth and heads to his truck and they drive off.