Ben Shockley, a hard-drinking Phoenix detective, Clint Eastwood is assigned to extradite witness Augustina "Gus" Mally Sondra Locke from Las Vegas. His superior, Commissioner Blakelock [Pat Hingle], calls her a "nothing witness" for a "nothing trial." Upon meeting Mally, he finds that she is a belligerent prostitute with mob ties and fears that both he and Mally are being set up. Shockley dismisses her concerns at first, but changes his mind when he learns that local bookmakers are taking bets on whether Mally will testify.
The car Shockley arranges to pick them up is bombed, and Mally's house is subsequently fired on by the police after Shockley is framed for kidnapping and attempted murder. Shockley and Mally hijack a county constable at gunpoint and force him to drive them across the border to Arizona. When the constable attempts to alert local authorities, he is gunned down by mob hitmen. Forced to camp for the night, Shockley stumbles across a biker rally and bluffs them into leaving, while also obtaining a motorcycle.
Blakelock is revealed to be responsible for the set-up; he is secretly in the pocket of the mob and had engaged in sadomasochistic sexual abuse with Mally, who had memorized his face. ADA John Feyderspiel is also shown to be involved as part of a conspiracy to thwart Arizona's prosecution of Vegas mobster Angelo Deluca.
While stopping in town for a meal, the two are ambushed by a police helicopter sent by Blakelock; Shockley lures it into an area filled with high-altitude power lines and the chopper explodes after striking a pylon. The motorcycle is disabled by a stray bullet, so they hop on a train, on which, coincidentally, the same two bikers whose machine they had "borrowed" are riding. The bikers beat Shockley and attempt to rape Mally. Shockley is only barely able to retrieve his gun and force them off. Shockley and Mally both realize that going back to Phoenix will be suicide, but it is the only way to prove their innocence.
Following a night together where they decide to marry, Shockley has Mally hold up a bus while he throws out the luggage. After reinforcing the driver's seat with armored plating, they drive into Phoenix using a route Shockley had purposefully mailed to Blakelock. Maynard Josephson, Shockley's former partner, warns the two of a gauntlet of armed police officers whom Blakelock has set up to "welcome" them. Josephson convinces Shockley to turn himself in to Feyderspiel, whom he mistakenly thinks will help them. As the pair follows Josephson outside, Josephson is shot dead by snipers from a nearby building, and Shockley is hit in the leg.
With no other option, the two return to the bus and enter the town. The bus is shot at as it runs the titular gauntlet of hundreds of armed officers lining both sides of the road, until it reaches the steps of City Hall, finally immobilized. Shockley emerges and begins to walk inside with Mally when Blakelock and Feyderspiel confront them. A panicking Blakelock grabs the nearest officer's gun and murders Feyderspiel, but runs out of ammunition before he can finish Shockley. Mally grabs Shockley's revolver and shoots the commissioner dead. Realizing Blakelock's crimes, the rest of the assembled officers watch as Shockley and Mally walk away safely from the gauntlet.
