The film opens on a quiet suburban home, where a babysitter is tending a young boy at night. A stranger comes to the door and asks to visit the boy, but the babysitter turns him away. While she secures the rest of the house, she is grabbed from behind and an unseen killer slices open her femoral artery. The killer goes upstairs and wraps the young boy in a blanket.
Three months later, a man and a cleaning woman are killed in a motel room in Amarillo, Texas. The man's femoral artery was severed and the woman's throat was cut. Longtime sheriff Buck Olmstead (R. Lee Ermey) is up for re-election. Both Olmstead and his opponent, city police chief Jack McGinnis (William Fichtner), are eager to be the one to solve such a big murder case before Election Day.
Meanwhile, Lane Dixon (Jared Leto), a hitchhiker, is picked up by Bob (Danny Glover), a drifter driving a white Cadillac Eldorado upholstered with pictures of naked women. Unnerved by the pictures, Dixon asks to be let out of the car at a miners' bar, which Bob warns against. Dixon is in the bar for a few minutes before getting beat up by a group of miners. Bob rescues Dixon and sends him out to retrieve the car. As Dixon drives them away, Bob reveals that he has slashed all the tires in the parking lot.
Back in Amarillo, FBI agent Frank LaCrosse (Dennis Quaid) arrives to inform Olmstead about his investigation of an elusive serial killer, whom he suspects is responsible for the motel murders. They track down the red SUV that was spotted driving away from the motel. LaCrosse confronts the owner, who has barricaded himself in an apartment and taken a family hostage. LaCrosse finds out that the man stole the SUV, and immediately deduces that he does not fit the profile of his killer. But his long criminal history, which includes previous violent crimes, makes McGinnis eager to pin the motel murders on the man. His lawyer reveals to LaCrosse and Olmstead that the man had stolen the SUV from an airport parking lot. Olmstead's men check the surveillance tapes at the lot and find the plates for a white Cadillac Eldorado, which belonged to one of the serial killer's victims. They put out an APB on the car.
Bob and Dixon are now in Colorado and the car is struggling with the elevation. At the next town, Martensburg, they stop at Shorty's Auto Repair. Shorty (Leo Burmester) is an old friend of Bob's, and they reminisce as Shorty fixes the car. Bob goes down the street to a general store to buy some candy corn. The teller gripes about having to mind the store as a storm approaches, making it clear that she is all alone. Bob follows her around the store and toys with a box cutter before propositioning the woman. Just as their interaction turns menacing, Dixon arrives to tell Bob that Shorty has fixed the car. Noticing a police officer leaving Shorty's as they approach the shop, Bob claims to have forgotten something inside. He kills Shorty while Dixon waits in the car.
Dixon drives them away toward the mountains. Bob assures them that they are ahead of the storm. When Bob takes over the wheel, he careens down the other side of the mountains. He tells Dixon about his son, and asks Dixon to look in on his boy as a sort of godfather, should anything happen to him. Bob gives Dixon the boy's address and then loses control of the car. Both men nearly die in the crash, but they escape before the car crashes off a cliff.
In Amarillo, the FBI has ordered Olmstead to keep LaCrosse in town until they arrive. They explain that he is assigned to another case in Philadelphia and that the investigation into the serial killer has been closed for months. LaCrosse reveals to Olmstead that the FBI believes the man who appeared on the porch before the little boy was abducted was the killer, because he committed suicide amid all kinds of evidence that linked him to the murders. LaCrosse believed it was too pat. He reveals to Olmstead that the abducted little boy is LaCrosse's son Andy. He shows Olmstead a picture of Andy that the killer sent him, which has a message on the back that reads, "2-18 To find him, you must kill me. To understand me, you must come to Believe." Olmstead then asks about the "2-18" reference, implying a date. LaCrosse says that it could be a date, or a reference to how many people have been killed. He reveals that the FBI had considered every interpretation without coming to a conclusion regarding the "2-18" reference. It is apparent that, if it referred to February 18, "2-18" is only a few days away.
When word reaches LaCrosse about Shorty's murder in Martensburg, Olmstead arranges for him to take a police helicopter to Colorado, even as he finds out that he has lost the election to McGinnis. Olmstead is placed in custody for violating the FBI's instructions. In Martensburg, LaCrosse is allowed to view the crime scene before being informally detained by the State Police. He surmises that Shorty, who was armed with a pistol, must have known his murderer.
Bob and Dixon manage to walk to a small town, where they crash in a hotel frequented by railroad workers. They all know Bob from the days when he worked on the railroads with Shorty. In Martensburg, LaCrosse realizes that "2-18" refers to a train number, and he frantically pursues the 218 as it heads into the mountains. He crashes a car into a river and barely manages to make it onto the train.
In the morning at Bob and Dixon's hotel, everyone is talking about the fact that the police are looking for a white Cadillac Eldorado upholstered with pictures of naked women driven by a young man who matches Dixon's description. Dixon confronts Bob at gunpoint, who denies any involvement in the murders. Bob explains that he bought the car for $500 cash from a stranger. Dixon calms down and joins Bob on a train, riding in the rear car with the snow scrapers and another friend of Bob's named Tex.
Aboard train 218, LaCrosse confronts a brakeman who boards the train. The brakeman explains that he is just catching a ride home, and he shows LaCrosse a map with a rail marker named "Believe". As LaCrosse sees the map, he is informed by the brakeman that "Understanding" and "Believe" are railroad sightings, thus explaining where the killer is headed by the references on the message. The brakeman explains that the only train headed towards Believe would be on the upper grade of the switchback. LaCrosse climbs the mountain to reach the upper grade, just as the train with Bob and Dixon comes into view.
On board, Tex asks if anyone has a light. Bob absentmindedly hands him a matchbook from the motel in Amarillo where the murders took place. When Tex remarks on the coincidence, Dixon looks at Bob in horror. Bob pulls out his knife and severs Tex's femoral artery, revealing that he has set up Dixon to be another fall guy for his crimes. The two of them fight with each other as LaCrosse boards the train. He arrives in the rear car after Dixon has subdued Bob and is tending to Tex. Believing Dixon to be the killer, LaCrosse does not pay enough attention to Bob, who comes to and attacks him.
During the final confrontation, Bob uses Dixon as a human shield and slices his throat before he and LaCrosse end up falling out of the train and onto one of the snowscrapers. LaCrosse grabs Bob before he can fall off the train, demanding to know where his son is. Bob reminds LaCrosse that he has to die first, and wriggles out of LaCrosse's grasp, falling to his death. Dixon writes the address that Bob had given him in the dust on the train floor, but when Olmstead and LaCrosse arrive at the location, it is an abandoned house. Just as LaCrosse is about to give up, he notices Andy playing in the yard next door and reunites with his son.Dennis Quaid as Special Agent Frank LaCrosseDanny Glover as Bob GoodallJared Leto as Dr. Lane Dixon M.D.R. Lee Ermey as Buck OlmsteadWilliam Fichtner as Jack McGinnisTed Levine as Deputy Nate BradenWalton Goggins as Bud (credited as Walt Goggins)Maggie Roswell as FaeAllison Smith as BeckyJulio Oscar Mechoso as Jorge MartinezKevin Cooney as Grant MontgomeryLeo Burmester as Clyde 'Shorty' Callahan
Switchback received negative reviews from critics and holds a 32% rating on Rotten Tomatoes based on 25 reviews. The film bombed at the box office, grossing just $6 million domestically off a budget of $38 million.
The dense plot was a point of confusion for many critics. Stephen Holden of The New York Times recounted several basic details of the plot wrong in his review. Holden describes the film as "a disorganized mess". He faults Quaid for being too dour and Glover for being too likable. But, both Holden and Roger Ebert had high praise for the film's atmosphere, especially its location shots. Ebert found the setting and the minor characters, like Ermey's sheriff, the most charming parts of the film, concluding, "What we have here is a potentially good movie swamped by the weight of Hollywood formulas it is forced to carry".