Mandy Lane Amber Heard is a standout student in a Texas town who unexpectedly becomes the center of attention among her male classmates over the summer. When the confident and popular Dylan Adam Powell invites her to a pool party at his house, she agrees on one condition: her best friend Emmet Michael Welch can come along. At the party, Dylan bullies and humiliates Emmet, and Mandy steps in to defend him, breaking the pattern of tension and showing she won’t stand for cruelty.
As revenge, Emmet convinces the drunken Dylan to jump from the roof into the pool, but the plan goes tragically wrong when Dylan misjudges the jump and hammers his head on the concrete, a fatal accident that changes everything.
Nine months pass, and Mandy has grown closer to many of Dylan’s popular friends, while Emmet endures intensified bullying. Their stoner classmate Red Aaron Himelstein plans a weekend party at his father’s remote ranch, and Mandy reluctantly accepts an invitation from Chloe Whitney Able, a popular yet insecure cheerleader. Mandy accompanies Red and Chloe, along with several other classmates—including the reserved football player Bird Edwin Hodge and the romantic couple Jake Luke Grimes and Marlin Melissa Price—to Red’s ranch. Upon arrival, they are introduced to Garth Anson Mount, the ranch hand who keeps a watchful eye over the group.
That night, Jake, offended by a joke, slips away to a nearby barn where Marlin performs oral sex on him. After another argument, Jake returns to the house, and an unseen assailant knocks Marlin out and breaks her jaw with the barrel of a shotgun. Back at the main house, Jake struggles to win Mandy’s attention, while anxiety over Marlin grows. In a misguided attempt to find her, Jake takes Red’s shotgun and pickup to search for Marlin, eventually discovering her by a remote lake. There, Emmet—seeking vengeance for the humiliation he suffered—confronts him and shoots Jake in the head, then breaks Marlin’s neck, killing both.
Emmet drives back to the ranch in Red’s truck and shoots fireworks at the porch, prompting Bird to chase after what he assumes is a prank. Emmet then confronts Bird, slashing his eyes with a knife and killing him. The rest of the group, intoxicated and exhausted, fall asleep in the house with Garth still nearby.
The next morning, Emmet wounds Garth with a shot, while Mandy tends to him. Red and Chloe rush toward Chloe’s car, but Emmet shoots Red and hunts down Chloe. In Garth’s shack, Mandy finds the bloodied knife Emmet used to kill Bird and heads outside, where Chloe is being chased. Mandy helps Chloe briefly, but then stabs her in the stomach, revealing that Chloe is in league with Emmet.
As Chloe bleeds, Mandy and Emmet discuss a suicide pact they had once planned. Mandy reveals she never intended to go through with it, believing Emmet joined the murders only to win her affection. Refusing to let her back down, Emmet prepares to shoot her, but Garth intervenes by wounding Emmet with a shotgun, forcing Emmet to stab him repeatedly. Emmet chases Mandy into the fields, and they fall into a ditch filled with cattle carcasses. Mandy seizes a log and fights off Emmet’s machete, ultimately killing him. She returns to an injured Garth, and the two drive away from the ranch, with Garth thanking Mandy for saving his life—perhaps under the assumption that she was also a victim.
A final flashback revisits a railroad track where the group paused during their drive. While the others joke around, Mandy balances on the tracks, quietly watching as she envisions her future victims.
