In a post-apocalyptic 2029, artificially inteligent machines seek to exterminate what is left of the human race. Two beings from this era travel back in time to 1984 Los Angeles: one is a Terminator , a cyborg assassin programmed to kill Sarah Connor . The other is Kyle Reese, a human resistance fighter sent to protect her. After killing two other Sarah Connors listed in the telephone directory, the Terminator tracks its target to a nightclub. Kyle saves Sarah from the Terminator's attack and the two make an escape.
Kyle explains that in the near future an artificial intelligence network called Skynet will become self-aware and initiate a nuclear holocaust of mankind. Sarah's yet-unborn son John will rally the survivors and lead a resistance movement against Skynet and its army of machines. With the Resistance on the verge of victory, Skynet has sent a Terminator back in time to kill Sarah before John can be born, as a last-ditch effort to avert the formation of the Resistance. The Terminator is an emotionless and efficient killing machine with a powerful metal endoskeleton, but with an external layer of living tissue so that it resembles a human being.
Kyle and Sarah are again attacked by the Terminator, leading to a car chase and their arrest. Lieutenant Ed Traxler and Detective Hal Vukovich tell Sarah that Kyle is insane. Kyle is questioned by psychologist Dr. Silberman, who concludes that he is paranoid and delusional. The Terminator attacks the police station and kills many police officers in its attempt to locate Sarah, but she and Kyle escape and seek refuge in a motel. Kyle confesses that he has long been in love with Sarah, having been given a photograph of her by her son John. Sarah reciprocates Kyle's feelings and they have sex.
The Terminator tracks them to the motel and wounds Kyle. In the ensuing chase the Terminator is caught in the blast of an exploding gasolinetank truck. With its external flesh burned away, it pursues Sarah and Kyle into a factory. Kyle jams a pipe bomb into its abdomen, blowing off its legs and one of its arms, but Kyle himself is killed. Still partially functional, the Terminator drags itself toward Sarah by its remaining arm. She leads it into a hydraulic press, which she uses to crush it, causing it to deactivate.
Later, a pregnant Sarah is traveling through Mexico. Along the way she records audio tapes which she intends to pass on to her unborn son John. She debates whether to tell him that Kyle is his father. A young Mexican boy takes a photograph of her which she purchases — it is the photograph that John will later give to Kyle. She drives on towards approaching storm clouds.