Two bicyclists cycling on a canyon are followed by a mysterious black car down the road. At the bridge, the car proceeds to crush one cyclist against the wall, and ram the other from behind, causing him to fall off the bridge. A hitchhiker, hoping to get a ride, encounters the car and insults it after it purposefully tries to run him down. In response, the car runs over him and leaves. The local sheriff's office, called to the first of a series of hit and run deaths, get a lead on the car that appears heavily customized and has no license plate, as pointed out by Amos Clemens (R. G. Armstrong) after he sees it run over the hitchhiker.
That night, in an apparent bid to kill Amos, the car instead runs over the sheriff, leaving Chief Deputy Wade Parent (James Brolin) in charge. During the resulting investigation, an eyewitness to the accident states that there was no driver inside the car, furthering Wade's confusion. Wade asks his girlfriend, Lauren (Kathleen Lloyd), who is a teacher at the local school, to cancel the upcoming marching band rehearsals for their safety. Lauren and her friend, who is Wade's deputy Luke Johnson's (Ronny Cox) wife, ask him to let them rehearse, to which Luke unwittingly agrees.
The car enters the town and attacks the school marching band as it rehearses at the local show ground. It chases the group of teachers and students into a cemetery. Curiously enough, the machine will not enter onto the consecrated ground as Lauren taunts the purported driver that any of the townsfolk have yet to see. Seemingly in anger, the car destroys a brick gate post and leaves. The police chase the automobile along highways throughout the desert before it turns on them, destroying several squad cars and killing five of Wade's deputies in the process. Wade confronts the vehicle and is surprised to see that none of his bullets put a dent on the car's windshield or tires. After trying to open the door (when it is revealed that the car has no door handles), Wade is knocked out and the car escapes.
That evening, Lauren, on her way home to pick up her things, is killed when the car jumps driving straight through her house and rams her, right when she is speaking to Wade over the phone. Luke puts forward to a grief-stricken and maddened Wade the theory that it acted in revenge for the insults hurled on it by Lauren and notes it cannot enter hallowed ground. Wade concocts a plan to stop the car by burying it beneath a controlled explosion in the canyons that lie outside of town. After discovering it waiting for him in his own garage, he is forced to carry out his plans post haste. He is pursued by the car into a mountainous canyon area where his remaining deputies have set a trap for the machine. In a final confrontation, Wade and Luke, at the edge of a cliff, bait the car into running straight at them, then jump aside as it goes over the cliff. With the dynamite detonated and the rubble falling on it, a monstrous demonic visage appears in the smoke and fire of the explosion, shocking the deputies.
The final scenes show Wade refusing to believe what the group saw in the flames, despite Luke's insistence about what he saw. The film concludes, in some cuts, with the car prowling the streets of downtown Los Angeles, clearly having survived.
Who insults the car?
the hitchhiker