Harold is a religious fanatic who pressures his family—his wife Betty and daughters Maggie and Sarah—to drink an unknown liquid, which is revealed to be poison. Maggie is the only one to fear death, and Harold later explains it was a test of faith for a future suicide pact.
The next day, Harold’s family is visited by three strangers: Fisher, Randy, and Luke who ask for help replacing a flat tire. Harold invites them inside, claiming his family lives several miles from civilization and without a phone. He offers to help and allows the group to stay for another day, but also discards their beer and rebukes their foul language.
At dinner, Fisher proves himself the most respectful of the trio and shares that he is moving to California from Chicago. After asking to use the restroom, Randy sneaks into Harold’s room to snoop around. Harold grows suspicious and searches for him, and the group discovers [Randy] in distress after a seizure.
Harold suggests that the best option is for the group to stay while Randy recovers, and Maggie begins to develop feelings for Fisher. Tension rises as Luke becomes anxious, and he later witnesses Harold taking a bath with Sarah. In the morning, Luke also learns Harold lied about having a car, and the group uses its tires to fix their vehicle. While they are outside, Fisher shows Maggie the inside of the car, and the two share an instant photograph that Maggie keeps as a memory.
After they depart, the group suffers another flat tire and returns to the house. Tensions flare when Luke launches a heated accusation, claiming Harold molests Sarah, and Luke is kicked out. Before leaving, Sarah hands him a bottle of poisoned lemonade, and he dies after discovering a spike strip that caused both of their car accidents. Back at home, Maggie notices that Randy has also died.
Maggie finds a note stating that she is from Nebraska. Fisher also uncovers several photographs of Maggie and Sarah from the past, showing them with other people. Together, Maggie and Fisher realize that Harold and Betty kidnapped the girls as their own after killing their parents. Inside, Betty overhears Harold and Sarah discussing their intimate relationship, and Fisher discovers Randy’s body. Harold arrives and knocks Fisher out with chloroform.
Back inside, Betty commits suicide. Tied up in a basement, Fisher is rescued by Maggie, and the two share a kiss as they attempt to escape, finding a crucified Randy and Luke; Fisher is then shot and crucified by Sarah. The group’s bodies are burned, and Harold declares that they were sacrifices for God. Discovering Maggie, Harold decides it is time for the family to complete their suicide pact. He hands his daughters glasses of poisoned wine, and Sarah willingly drinks and dies. Maggie refuses and watches Harold drink from an unpoisoned glass before striking him with the wine bottle. Armed with a handgun, Harold pursues Maggie, who cuts his ankles and slashes his neck. The next morning, Maggie gazes out toward the horizon.
