Terminator: The Sarah Connor Chronicles, FOX
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Caution: potential spoilers (including of the first two movies in the franchise).
This is based on the Terminator movie franchise, which began in 1984 with "The Terminator," though I didn't see that until some years after I'd seen the sequel, which came out in 1991. Then there was a third movie in 2003, but it's part of a different timeline than this series (which ran for two seasons from 2008-09). So, you don't need to worry about anything other than the first two movies, before seeing this show. At the time that I watched this, I didn't clearly remember any details of the movies, but at least I had a fair grasp of the premise, and I was able to look up a bit of backstory online to refresh my memory. And I'll share a bit of the backstory, here:
In 2029, the world is controlled by machines. There's this artificially intelligent computer called Skynet, which went online in 1997, and triggered a nuclear war to wipe out humanity. Of course it was not completely successful, and humans continued to fight, but Skynet made cyborgs programmed to kill humans. Eventually there was a resistance group led by a man named John Connor, who was on the verge of defeating the machines. So, in the first movie, Skynet sent a cyborg back to 1984 to kill John's mother, Sarah Connor, before she conceived him. But John sent one of his men, Kyle Reese, back in time to protect her. The second movie is set in 1995, when John is 10 years old. (Spoiler: Kyle Reese is his father, but he died at the end of the first movie). Another cyborg is sent back to kill John, and there's a cyborg sent to protect him, as well (the one protecting him now looks like the one who tried to kill Sarah in the first movie, confusingly enough). Ultimately, the good guys destroy some technology that would eventually have led to the creation of Skynet.
Now, this series starts out in 1999, when John is 15. Sarah and John (played by different actors than in the movies, of course) have been on the run ever since the events of the second movie, always in hiding, always using different aliases. Sarah (Lena Headey) is involved with a man named Charley Dixon, who proposed to her. And so she decides she and John (Thomas Dekker) must leave (not wanting to involve him in their troubles). When they start another new life, in another new town, John meets a girl at school named Cameron Phillips (Summer Glau). But she turns out to be a cyborg sent by the future John to protect him and his mother. There will be more Terminator cyborgs showing up to try to kill them (most notably one called Cromartie), and the FBI is also looking for them (believing Sarah killed a scientist during the events of T2). The agent in charge of finding her is James Ellison. At the end of the first episode, Cameron takes Sarah and John through time to the year 2007, and everyone thought they died in 1999... until they reappear 8 years in the future.
Skynet, obviously, will still be created, but it doesn't go online in 1997. Because of the events of T2, Skynet's activation, and the nuclear war, were delayed until April 2011. Now there are other resistance fighters from the future who have been sent to the past, who set up a safe house, but they were all killed. Except Derek Reese (Brian Austin Green), the brother of Kyle (and so, John's uncle). He eventually teams up with Sarah, John, and Cameron, toward the end of the first season. And other terminators have been sent back with specific missions, not related to killing John or Connor, but rather the resistance fighters, I guess. But if they discover who John is, of course they'll try to kill him.
Anyway, Sarah, John, Cameron, and Derek, will have to try to survive, but they also want to try to fight Skynet itself, prevent its creation. There are all sorts of divergent storylines relating to this, various people instrumental (even if unwittingly) in Skynet's creation, who must be stopped. And other people who must be protected, and sometimes our heroes aren't sure which is which. Nor can they ever trust anyone, because anyone they meet could be a cyborg from the future. So... life is tough, and John has never had a normal childhood, to say the least. Which takes its toll, psychologically.
Well, we see a bit more of Charley Dixon and his new wife in season 1 (he had gotten married when he thought Sarah was dead). And a bit more in season 2. Also in season two, there is a new character named Catherine Weaver (played by Shirley Manson of the band Garbage), the head of a corporation called ZeiraCorp. She's a terminator, who can morph (like the bad terminator in the second movie did), but she seems different from any other terminators we've seen, and so far I haven't really got her pegged. She's not good, but I'm not really quite sure what her motives are. Also, she has a young daughter named Savannah, whose father died some time ago, and seems to realize her mother... isn't the same as before. It seems as if the terminator replaced the real Catherine Weaver, though Savannah doesn't realize anything like that. Anyway, Ellison learned the truth at the end of the first season, so now he's sort of on Sarah and John's side, though he has no contact with them. The important thing is he believes in the existence of terminators. He no longer works for the FBI, but he gets recruited by Weaver to search for robots. She clearly isn't telling him all she knows, nor does he tell her everything he knows. Meanwhile, she's trying to build her own A.I., using her corporation's resources....
Well, lots of stuff happens in the second season. There is a woman named Jesse, a former lover of Derek's from the future, who shows up in the present. Of course, since any actions taken in the present can alter the future, she's not quite the Jesse he knew, and vice versa. Still, they hook up, and he doesn't tell John and Sarah about her. Meanwhile, Jesse has a girl named Riley, also from the future, working for her, getting closer to John, for some reason. They become friends, and then a couple, sort of, though no one really trusts Riley. They certainly don't know the truth about her, though. Also, Cromartie is eventually... well, the chip containing his programming is destroyed. But his body is taken by Ellison, and Weaver ends up hooking it up to her A.I. (called John Henry), whom she wants Ellison to teach... morals, or whatever. And... you know, there are stand-alone stories as well as the ever-progressing over-arching story, and different plotlines could intertwine, or not... it's all rather complicated.
I also wanted to say there are sometimes different storytelling techniques employed, which I always quite enjoy. However it's told, the story is always fascinating... I wish I could say more, but the season ends on a really intriguing cliffhanger, and then... there was no third season, which really sucks.