Ruby, a young female in a feral, desert family, brings stolen goods to her Grandpa Fred’s rural gas station, Fred’s Oasis, but Fred says he has no food to trade. When Ruby sees that Fred has loaded his belongings into a pickup truck, she asks if she can leave with him, but at that moment a station wagon pulling a mobile-home trailer stops for gasoline, so Fred hides Ruby and goes outside to dispense gas. The tourists are driver Big Bob Carter, a retired policeman, his wife Ethel Carter, their son, Bobby Carter, their daughters Brenda Carter and Lynne Wood, with her infant, Katy, and husband Doug Wood; along with two German shepherds, Beauty and Beast. Big Bob asks Fred about a local silver mine that he and Ethel inherited, but Fred says the silver mines were defunct long ago and the desert is now an Air Force firing range. He advises the family to resume their journey west. When Bobby, accompanied by Beauty the dog, uses the bathroom, Beauty senses something nearby, but Bobby returns to the family trailer. After the Carter family pulls away, Fred’s pickup truck explodes and Ruby’s brother, Mercury, pulls her away, saying that Papa Jupiter will be angry that she tried to leave. At the wheel of the station wagon, Big Bob is unnerved by fighter jets roaring low overhead, and when he swerves to avoid hitting a rabbit, he breaks an axle. Watching the Carters assemble outside the trailer, Pluto, another of Ruby’s brothers, radios ahead to Papa Jupiter on his Air Force walkie-talkie. The Carters cannot get anyone on their citizens band radio, so Big Bob gives one of his two pistols to Bobby and tells the boy to guard the family while he and Doug go for help. Doug walks ahead while Big Bob returns to Fred’s Oasis. After the men leave, Beauty reacts to something in the hills nearby and runs off, with Bobby following. By the time Bobby finds Beauty, the dog has been killed and gutted, and as Bobby runs back to the trailer, he trips and is knocked unconscious. Meanwhile, the Carters’ other German shepherd, Beast, breaks his chain and runs into the hills. As night falls, Lynne calls for help on the C.B. radio and hears heavy breathing. Bobby returns to the trailer, but he is too concerned about family morale to report Beauty’s grisly death. Meanwhile, Big Bob reaches Fred’s Oasis and finds the old man trying to hang himself with the mistaken presumption that someone else is coming to kill him. Fred tells Big Bob that the Carter family is in danger from a pack of humans living nearby. He explains that his wife, Martha, bore a mutant son who slaughtered animals, burned down their house, killed Martha and a younger sister, and kidnapped a prostitute to start a family of feral children. Suddenly, Papa Jupiter smashes a window, grabs Fred, and yanks him outside into the darkness. By the time Big Bob pulls his gun and runs outside, Fred is dead, Papa Jupiter has gone, and the telephone is disabled. As Big Bob runs back toward the trailer, he hears taunts from nearby, and falls down with chest pains, while two figures approach and take his gun. Meanwhile, Doug returns to the trailer and reports finding only an Air Force dump filled with old military equipment, including a spool of cable that he has carried back. Elsewhere, Ruby is chained in a cave and forced by her mother to eat Beauty’s guts as punishment for trying to run away. Later, Doug and Lynne make love in the station wagon, while the others sleep in the trailer. Pluto silently siphons gas from the vehicle’s tank. Hearing dog sounds, Bobby searches for Beast outside as Pluto sneaks into the trailer. Locking the door, he gathers food, bullets, and a hatchet, then sexually attacks Brenda in the tiny bedroom while Ethel sleeps in the main room. Bobby returns, finds the door locked, and rouses Doug and Lynne in the station wagon to retrieve their spare key. When they complain, Bobby admits finding Beauty’s gutted carcass earlier. Meanwhile, in the darkness, Jupiter and Mars crucify Big Bob and soak him with the gasoline from the station wagon. When Pluto radios them from inside the trailer to “Do it,” they torch Big Bob, creating a bonfire, which draws Doug, Bobby, Lynne, and Ethel, who try to save him. Inside the trailer, Mars pulls Pluto off Brenda and rapes her. When Big Bob dies, Bobby runs looking for revenge, while Ethel and Lynne return to the trailer. When they see the strangers with baby Katy, Lynne fights Mars and stabs him with his own knife, but Mars shoots both her and Ethel dead with the gun he took from Big Bob. He and Pluto flee with the baby, warning Brenda that he will come back for her. In a den, Papa Jupiter celebrates the meal that baby Katy will provide, and asks Mars if he killed everybody at the trailer as ordered; he is angry to learn that three survived. Meanwhile, Beast pushes Mercury to his death from a high rock, picks up Mercury’s walkie-talkie in his teeth, and carries it back to the trailer. By eavesdropping on the radio, Bobby and Doug learn that the feral family is coming to get them. Doug and Beast hide in the hills and see Jupiter and Pluto walking toward the trailer. While Doug tries to warn Bobby on the C.B., Bobby calls for help. Jupiter pretends to be a highway patrolman and Bobby unwittingly admits that he is down to his last two bullets. Meanwhile, Beast attacks Pluto, mangling his foot, and Jupiter calls back to Mars, telling him to kill the baby, but Ruby has snatched Katy and run away. Jupiter races ahead toward the trailer to kill everybody. Doug and Bobby place Esther’s body in a lawn chair away from the trailer, attaching one end of a cable to the back wheel of the station wagon, and tie the other end in a loop near Esther’s body. When Jupiter approaches Esther’s corpse, Bobby puts the station wagon's transmission in gear, catching Jupiter’s foot with the cable and dragging him toward the vehicle. When Jupiter gets loose, he chases Bobby, Brenda, and Doug into the trailer, but they climb out the back window and blow up their propane tanks, killing Jupiter. Although Doug attacks Mars, he appears to be overwhelmed until Ruby grabs a rattlesnake and lets it bite Mars’s neck, permitting Doug to stab Mars to death.