The best time-travel show of all time is streaming for free right now

Back to the Future and Doctor Who are both great time travel stories for the same reason: anachronisms. Taking fictional characters and dropping them somewhere in time they don’t belong can be equal parts hilarious and tragic depending on how it’s played, but this basic fish-out-of-water concept is as important to science fiction as robots or ray guns.

One of the biggest hurdles time travel stories face is figuring how an unstuck-in-time character can blend into historical settings. In 1989, the unmatched sci-fi classic Quantum Leap solved this problem with a simple twist: What if you time traveled by jumping into the bodies of other people who lived in the past?

Starring Scott Bakula as Dr. Sam Beckett, Quantum Leap did something deftly unique with time travel, and it’s never been topped since. Here’s why the show is an enduring sci-fi classic worth rewatching (or watching) right now — especially since it’s currently streaming for free online.

Trying to figure out the actual sci-fi rules of Quantum Leap is a bad idea. As stated in the voice-over, Sam Beckett “stepped into the quantum leap accelerator and vanished.” The premise of the series is that his consciousness is transferred into various people’s bodies — regardless of gender — throughout time. Once Sam shows up in one of these bodies, a holographic projection from his associate Al (Dean Stockwell) advises him on what he’s supposed to accomplish in whatever historical period he’s found himself in.

Basically, Quantum Leap is a paint-by-numbers science fiction drama. Every episode begins with Sam trying to acclimate to his new body, while Al tells him the stakes. Despite the fact that Al is assisted by a super-computer named “Ziggy,” there’s never a clear path for what Sam is supposed to do. His essential mission — which is ill-defined — is to “set right what once went wrong” — but what that means exactly is relatively opaque until the end of each episode. This makes zero sense. It’s also brilliant.

Each episode of Quantum Leap creates a ticking clock plotline in which Sam is supposed to correct something that was previously wrong with the timeline. This notion is loosely defined, which is narratively super-convenient. Al frequently only has just enough data to get help Sam figure out what he’s maybe supposed to “fix,” but not enough info to tell him how to do it. The best example of this is probably contained in the show’s most proactive episode, “Lee Harvey Oswald,” a two-parter in which Sam leaps into, you guessed it, Lee Harvey Oswald.

In the first part of this episode, Sam grapples with his mind being taken over by Oswald, as well as the idea that perhaps he wasn’t sent to this time period to prevent anything, but instead to figure out if Oswald really was the lone gunman. After several red herrings, the ultimate solution is (spoiler alert!) that Sam is there to prevent the death of Jackie Kennedy, who, in the alternate universe everyone is apparently living in, was also shot along with JFK.

This is easily the most over-the-top example of the way a Quantum Leap storyline can go, but it’s a great way to think about the series. The twist in this particular story was similar to many other episodes of the show — Sam isn’t really there to save who he thinks he’s there to save — but, the twist relies on a change of context rather than a story turn. You can’t really get away with this in non-science fiction shows.

But what makes Quantum Leap so fascinating as a time travel show is that it’s the exact opposite of most time travel stories.

From the best time travel episodes of Star Trek to Back to the Future, the conflicts inherent in 9 out of 10 of these stories are all about not changing history. Patient zero for this kind of time travel cautionary tale is arguably Ray Bradbury’s short story “A Sound of Thunder,” in which one prehistoric butterfly flapping a different way alters the entire course of history.

But Quantum Leap is a giant middle finger to that time travel tradition. Every single episode of the show is explicitly about Sam messing with the timeline, rather than keeping it the way it was. (Ironically or not, when Scott Bakula later starred in Star Trek: Enterprise, the entire premise of that series began with the notion of a temporal cold war, designed to subvert history, complete with people leaping back in time.)

The funny thing is, the show is almost never discussed as an anti-time travel standard. But in its bones, it’s a very subversive science fiction show that bucks nearly every tradition of time travel in the genre, a premise it passes off casually. Quantum Leap doesn’t feel like a radical sci-fi series because it’s a very mainstream cozy 1990s series. If you tuned into an episode mid-way through, you might not even know it was a show about time travel. Sometimes Sam is just helping people fix up a farm for 45 minutes.

The way Quantum Leap gets away with its risky time travel premise is partly because Scott Bakula is the most instantly likable accidental sci-fi hero of all time. Sam is just a rock-solid guy, and his internal conflicts (rarely) have anything to do with the situations he’s thrust into.

There’s an overall existential thrust to Sam’s journey. He always hopes that “each leap will be the leap home,” stating outright that if the show is going to continue, Sam is going to have to stay forever adrift, jumping from body to body, looking in the mirror every week and seeing someone else.

These days, you can’t imagine Quantum Leap because the show is oddly lighthearted despite its heady premise. But, when Sam says “Oh boy,” every time he finds himself in a new body, in a new time period, it’s super endearing.

Leaping back to the 1990s, when this kind of high concept science fiction could also be done with a light touch, seems almost impossible. For science fiction like Quantum Leap to happen again, the goal of TV would have to change. These days, Sam would have to be involved with huge season-long arcs in which every single leap created a larger story. Back then, one leap at a time was enough.

Quantum Leap is streaming totally for free on the NBC app.