Just outside of Monument Valley, Arizona, Vietnam War Marine veteran John Wintergreen, a highway patrolman, joins his partner, Zipper Davis, patrolling lone desert roads on their Electra Glide motorcycles. Although John, who has requested a transfer three times in hopes of rising to detective, finds the work dreary and unchallenging, he nevertheless remains dedicated to enforcing freeway restrictions, while the indifferent Zipper declares that his only goal is to save enough money to buy a fancy motorbike. One afternoon, the partners stop a Volkswagen bus painted in psychedelic colors and Zipper, bored and hostile to the hippie driver, goes so far as to plant marijuana on the driver in order to make an arrest. Although disagreeing with his partner’s action, John remains silent. Later the men find Willie, a local old man, wandering in the desert far from his rundown shack, insisting that his roommate, Frank, is dead. When the patrolmen investigate, John suspects the apparent shotgun suicide is actually a murder and makes copious notes that the police coroner later ignores. After detective Harve Poole concurs that the death requires an investigation, he assigns John to be his new driver and vows to make him the next best investigator in the state. Elated to shed his patrolman uniform for a detective business suit, John joins Harve at a bar where Harve introduces him to the “winners circle” of police detectives and cautions him about the “police genocide” currently being enacted by a law-hating public. The next day, John and Harve question Willie at a rest home and the old man reveals that Frank, who had begun inviting young people to the shack, was likely killed for the $5,000 he had stashed there. On the way to investigate the shack, Harve tells John to learn to listen to his inner voice as the best way to solve crimes. At the shack, Harve explains that they are looking for something that does not belong in the setting and, finding a pristine statue of the Virgin Mary, breaks it and discovers it is packed with illegal narcotics. When an examination of fingerprints in the shack reveals those of recently paroled drug dealer Bob Zemko, Harve declares the dealer is likely the murderer and thief of the missing $5,000. Visiting a nearby hippie commune, Harve sends John inside where he politely asks about Zemko and, after receiving no answers, thanks the group then reports to Harve. Dubious, Harve then roughly questions the group of hippies, striking several and choking one young man in a headlock until a young woman admits she has seen Zemko. Later that evening, Harve takes John to a closed bar where he introduces him to his girl friend Jolene, unaware that she and John have been having an affair. Bitter about her failed career as a show girl, the drunken Jolene mocks Harve and reveals her relationship with John, praising his sexual abilities in the face of Harve’s impotence. On the drive back to Harve’s home, the stunned detective insists that Jolene’s drunken rambles were lies, then explodes at John for sleeping with her and demands that he tell no one of her accusations. John is immediately sent back to patrol duty and a day or two later, he and Zipper follow a group of motorcyclists heading into the neighboring town. When John recognizes Zemko, the police give chase and in the ensuing pursuit several bikers are injured in crashes. When Zemko continues to evade the patrolmen, a frustrated Zipper takes aim at him with his pistol, but John kicks over his partner’s bike, then forces Zemko to drive through the window of a diner. At police headquarters, when Zemko refuses to tell Harve and John how he came to be carrying $1,000, Harve threatens to beat him up in a manner that will leave no outward bruising. Uneasy with John’s presence, however, Harve sends Zemko away. After working security duty at a large rock concert, John reflects that he should act on his instincts about Frank’s murder. Returning to Willie and Frank’s shack, John gently approaches the old man and asks him if he killed Frank. Relieved to be able to confess, Willie explains that after being friends with Frank since World War II, he was dismayed when Frank abandoned him to make friends with several young people. Acknowledging Willie’s loneliness and assuring him of his worth, John promises to visit him wherever the authorities place him. Later, after Willie is taken away under arrest, Harve arrives and questions John, who says he concluded that Frank only started dealing drugs to make friends and that Willie reacted out of simple jealousy. Unconcerned whether Frank really ever had $5,000 or not, John accuses Harve of using brutality and intimidation for selfish reasons rather than truly considering the facts in the case. The next morning, John visits Zipper at his dilapidated, tiny RV home and when his drunken partner displays a shiny, new, chrome-covered motorcycle, John realizes that Zipper stole Frank’s money. Appalled that Zipper would have let Zemko go to jail for the theft, John berates him, but Zipper justifies himself by claiming he has no hope working in the dead-end, thankless, low-paying job of a highway patrolman. Knowing the principled John will turn him in, Zipper drunkenly pulls his gun and fires at John from close range. Pleading with his friend to stop, John draws his gun after Zipper fires a third time, and shoots him. Some time later John patrols the barren desert alone and stops a speeding, psychedelic-colored van. Recognizing the driver from his license as the man he stopped earlier, John lets the man and his friend go. Realizing that he has forgotten to return the man’s license, John speeds after them on his Electra Glide, but fearful of being searched, the driver’s partner shoots John, who dies on the barren desert highway.