Filmed in Chloride, Arizona.
Frank "J. J." Weston (Bruce Dern) meets a high-school mate, Paul Collier (Cameron Mitchell). JJ hangs out with a gang of motorbike riders, but Paul is a successful architecht in LA. Paul is following Karen (Diane Ladd), an ex-lover pregnant with his child.
The riders (Jack Nicholson, Neil Burstyn-Nephew, Phil Carey, Earl Finn, Lou Procopio...) meet at the canteen, where they dance and make too much noise. Barmaid Carmela, (Helena Clayton) calls Ringo Álvarez, (Harry Dean Stanton), the local sheriff. Ringo has to convince Pancho, his fat, lazy deputy, to help him finish the mayhem. Ringo tells them to go away. They leave, but stay at a beach nearby.
Paul wants Karen to have an abortion, but she refuses. So he asks to her to marry him. She wants to have the baby and stay single. He wants to have fun; she wants to settle down. Their car breaks down, and the riders frighten them. JJ saves the couple.
Later on, some riders attack Paul, who defends Karen. Frank saves them, but as a consequence, Paul needs a doctor badly. The riders want to rape Karen. Paul runs away. Just to win some time for Paul to bring the sheriff, Frank proposes a race, and whoever wins can have sex with Karen, although she doesn't agree to that.
Paul contacts the sheriff's officer. Only Pancho and a priest are there, and they're so afraid that they won't help Paul. Paul goes to the canteen, where nobody wants to help him, and Carmela tells him to go away. Outside the canteen, a gentle boy tells him to follow him as he knows somebody who can help. The boy takes Paul to Miguel (Robert Dix), a Mexican farmer who's celebrating his birthday. Miguel's daughter (Rita Reinhardt) goes out to the beach on her own for some dumb reason, where she's assaulted by the bikeriders. Miguel, Paul and more Mexican people go to rescue Karen and Miguel's daughter.
The race had already taken place. JJ performs a mock-marriage ceremony for the winner rider and Karen, reading an instructions manual for Harley Davidson motorbikes. Paul blacks out as soon as the rescuing team reaches the riders (that's a cavalier!).
Frank and the winning rider fight, telling everybody else not to get between them, avoiding a bloodbath. When Frank wins, the riders promise to go away. Because of everything which has happened, Frank doesn't feel like a rider anymore. He just wanted to have fun, not to kill somebody.