Old science fiction often looks out of date; past predictions can seem awfully corny when you're actually living in the future. “Terminator: Dark Fate,” though, manages to fit its old clunky rotors and cogs smoothly into the socket of our apocalyptic present. This film doesn't have the inventive genius or perfect, remorseless follow-through of the first two “Terminator” movies from some three decades ago. But it does show how the worst and the best versions of our future keep advancing — just like this franchise.

There have been a lot of abortive, mediocre “Terminator” sequels over the last 28 years, most recently the self-parodically convoluted and atrociously named “Terminator: Genisys” (2015). “Dark Fate” wisely erases all these bad ideas from the timeline, and instead picks up as if the classic “Terminator 2: Judgment Day” (1991) was the last canonical release.

This film doesn't have the inventive genius of the first two “Terminator” movies from some three decades ago. But it does show how the worst and the best versions of our future keep advancing.

Arnold Schwarzenegger is back, showing once again that he's the only actor who can turn a killer robot into comic gold. ("I am very funny," he deadpans, and you laugh because it's true.) The wonderful Linda Hamilton, as sinewy and imposing as ever, returns for the first time since “T2.” So does director James Cameron, who signed on to the film as a producer, and seems to have managed to bring at least some of his old battery-powered magic with him.

In “T2,” Sarah Connor (Hamilton) averted a nightmare future in which an artificial intelligence named Skynet nearly wiped out the human race in 1997. But while that Armageddon didn't happen, saving the world once doesn't save it forever. By 2020, scientists have managed to develop a different AI called Legion, which unleashes a similar age of the machines sometime in the following two decades.

Humans fight back, and so Legion, like Skynet, uses time travel technology to send an android terminator (Gabriel Luna) into the past to kill key resistance figures — in this case, Dani Ramos (Natalia Reyes). The resistance in turn sends back an augmented human named Grace (Mackenzie Davis) to protect Dani. Soon Grace and Dani are joined by Sarah Connor, and by an aging Skynet Terminator (Schwarzenegger), who has developed human emotions over the years, calls itself Carl and is passionate about drapes.

The backstory sounds complicated, but this is the first time since "T2" in 1991 that the franchise has really captured the simplicity of the original films' plot dynamics. The good guys run. The Terminator chases them. There are spectacular violent clashes, in which the Terminator is spindled, shredded, exploded and lit on fire before it picks itself up and comes after its targets again. That's the formula, and “Dark Fate” follows it to a T, with a full complement of enormous guns, sledgehammers and giant exploding vehicles, some of them airborne.

The action/slasher cyborg mechanics are well done. But where the new film really excels is in its retooling of the franchise's thematic obsession with that title phrase — dark fate.

The action/slasher cyborg mechanics are well done. But where the new film really excels is in its retooling of the franchise's thematic obsession with that title phrase — dark fate.

“T2” used its time travel conceit, not to emphasize the inflexibility of destiny, but to insist on the consequence of human choice and free will. The Terminators seem unstoppable. But they aren't, and neither is the nightmare future they embody. "Dark Fate" has that faith as well. "You taught us that the only fate is what you make for yourself," Grace tells Dani. Humans can create a future of war, genocide and cruelty if they choose. Or they can take another path. Legion, as Dani says, is just a machine. Humans created it, and humans can take it apart.

The terrible future “T2” was specifically obsessed with in 1991 was nuclear holocaust. Skynet was a defense computer that precipitated the nuclear war many feared would end the Cold War; the most powerful sequence in “T2” is a terrifying dream vision of a playground incinerated by an atomic blast.

When the Soviet Union peacefully dismantled in the early 1990s, it erased one possible, particularly dystopian future. “T2” was a kind of violent pulp celebration of this new and unexpected peace.

We're now a full generation from the end of the Cold War, and that era's expansive possibilities have curdled. The far right is on the rise across the globe; fear of nuclear winter has been replaced by fear of global warming. We avoided Skynet only to have Legion come for us.

You could see the new movie as a call to optimism. We beat the end of the world once, so we can do it again. But “Dark Fate” isn't an especially cheery film. It starts with the brutal, meaningless murder of one of the main protagonists from “T2,” and other major characters die throughout the film with a determined, unflinching regularity. It's surprising the survivors aren't completely paralyzed with PTSD by the conclusion

And that conclusion is itself ambivalent. The movie insists that fate can be changed. But there's no guarantee that it will be. People suffer and die for a better world they'll never see, and which may not even come. Legion or something like it is still waiting five minutes from now, or even closer.

“Dark Fate” doesn't tell us that we will always avert the apocalypse. Instead, it says that the worst future is already here, hunting us. The terrifying scenes of Legion's armies murdering helpless humans resonate because armies have already done that and still are.

You can despair. Or you can take what you have — grief, pain, maybe a beloved character actor or two — and try to make something better. The future, like the present, is always both a nightmare and a dream, depending on what we decide to make it.