The date is May 12, 1984, and on this day, two naked men arrive in Los Angeles.
Wow, now that we've written that out…
One of these guys kills three street punks and steals their clothes; the other is chased through a convenience store by the police. Nothing too out of the ordinary for Los Angeles, really, except that these men are time-travelers.
Both men secure guns and look up a woman named Sarah Connor in the phonebook. Hey, kids, remember phonebooks? No? Makes you wonder how two guys from 2029 knew about them, doesn't it? Anyway, the buff time-traveler visits the first Sarah Connor listed and murders her, expending more bullets than he does words.
Cut to the other side of town, and we see another Sarah Connor suffering through a terrible, horrible, no good, very bad day. She's bad at her waitressing job, her customers are rude, and her date cancels on her because, like her bestie Ginger says, he's a bum, even if he does drive a Porsche. Preach it, sister.
Not one to let a bum ruin her night, Sarah goes out for a slice when she sees a news report that somebody is murdering Sarah Connors across L.A. Reasonably freaked, she goes to find a payphone (remember those?), and the smaller time-traveler stalks her all creeper-like. She ducks into a night club named, no joke, the Tech Noir. Seriously, this movie is so '80s.
Unable to contact the police, Sarah calls Ginger for a ride. At their apartment, the buff time-traveler murders Ginger and her boyfriend. He's about to leave, believing his job complete, when he hears Sarah leaving a message and telling Ginger exactly where she is. It's the worst example of poor timing since Juliet woke up from her cadaverous nap moments after Romeo took a hit of poison.
Sarah calls the police again, and Lieutenant Traxler, who has been assigned the Sarah Connor killer case, promises to send a squad car. She waits, but the buff time-traveler arrives and aims to kill her. She's saved by the smaller time-traveler, who pumps a bunch of shotgun shells into the big guy. He and Sarah run, but the buff time-traveler, undeterred by something as annoying as a chest cavity filled with 12-gauge slugs, pursues them.
They escape, and the smaller time-traveler gives Sarah the 411. His name is Reese, and he's been sent from the future to protect her from that other guy. Only the other guy isn't a guy: it's a cyborg, a machine dressed in human flesh whose sole purpose is to kill Sarah.
Why? Good question. In the future, the collective fear of all senior citizens has come true, and those gosh-darned gadgets and gizmos have risen up against humanity. But Sarah's future son, John Connor, will teach humanity to rage against the machines, and he will lead it to victory. The Terminator killing Sarah will ensure that John is never born.
After another car chase, Sarah and Reese are apprehended by the police. A criminal psychologist, Dr. Silberman, interviews Reese, determining the man is several Pokémon short of a full Pokédex. While Sarah rests and Reese is in lockdown, the Terminator arrives. It assaults the police station and kills every police officer in the building. Sarah and Reese only escape by committing a third act of grand theft auto, which has got to be a one-day record, even for L.A.
Sarah and Reese spend the night under an overpass. Reese elaborates about the dark, dystopian world of tomorrow, as well as Sarah's role in it. She doesn't believe she could possibly be the person he claims she is.
The next day, Sarah and Reese hole up in a hole of a motel. While Reese goes shopping for supplies, Sarah showers and calls her mother. She tells her where they are hiding, but the camera reveals to the audience that it's really the Terminator doing a spot-on Mom impersonation.
Sarah and Reese spend a romantic day making homemade explosives. That night, Reese reveals that he loves Sarah and came across time to protect her. They get busy between the sheets. Reese did shower and launder that homeless guy's pants beforehand, right? Right?
The Terminator busts in on the lovers, but Sarah and Reese escape after yet another act of grand theft auto. The Terminator gives chase and shoots Reese. Sarah crashes the stolen truck into the Terminator, causing her to flip it. Not a machine to be one-upped, the Terminator steals an 18-wheeler and tries to run them down. Although injured, Reese plants an explosive in the semi, destroying it in epic fashion.
Sarah and Reese embrace, thinking the battle is over. Guess they have never seen a horror movie—otherwise they would know that the monster always rises again. And rise it does. The Terminator strolls from the fire like a mechanized Grim Reaper and pursues our heroes into a factory.
After a deadly game of hide-and-seek, the Terminator traps Sarah and Reese on a walkway. Reese uses his last explosive to blow up the Terminator. The blast injures Sarah and, sadly, kills Reese. But the Terminator is still not done. Its upper half crawls after Sarah. After a desperate, crawling escape, she traps it under a hydraulic press and crushes it into sheet metal.
Sometime later, we see Sarah driving through Mexico. She is pregnant, and it's revealed that Reese was John's father the whole time. It's time-travel, people. Just don't think about it. A boy takes a picture of her, the same one Reese had in the future. Sarah goes into hiding to prepare for the future she knows is coming.