Foundation Season 4: Every Book Storyline That Could Happen Next

Major spoilers ahead for "Foundation" season 3, episode 10, "The Darkness."

"Foundation" season 3 is complete. The Genetic Dynasty has fallen. The Mule has been revealed. The Second Foundation is victorious. The Seldon Plan is set back on its course. So, what's next for Apple TV+'s mind-bending sci-fi adaptation? "Foundation" is based on five books and two prequels written by Isaac Asimov. They're also set in the same universe as Asimov's robot novels. This gives us plenty to draw on to see what happens next.

There is one caveat, though: The specific direction of the show is very much up in the air at the time of this writing. "Foundation" has been renewed for season 4, so that much is certain. Where will it go in the next season? That's up for debate. Why? Because showrunner David S. Goyer is not attached to the show anymore. Goyer ran the first two seasons and authored around 85% of the third season. However, he has made it clear that he is not involved in season 4, and the new creative team is charting their own path. He said as much in a Q&A in August 2025, where he explained:

"I haven't written any scripts for S4. I did have an overall plan, but I don't believe the new team is adhering to any of those ideas. They are charting their own path and making it their own, as they should."

Without his creative direction, things could take any number of twists and turns moving forward. Of course, with or without Goyer, Isaac Asimov's source material remains the obvious point of reference to at least get a general idea of what could happen next. Having read through the "Foundation" compendium of books not once but twice in recent years, here are the top things that came to my mind as far as what could happen next in the show.

First, we need some resolution. Bayta is the Mule. Great. Cool twist on the original book plot (where Magnifico Giganticus is actually the Mule all along). Showrunner David S. Goyer's explanation for using Bayta as the bait-and-switch reveal makes sense. But what comes next? If you recall, the fading moments of season 3 had Gaal Dornick (Lou Llobell) and Bayta (Synnøve Karlsen) duke it out, one mentalic against the other. Gaal had some backup in the form of the Second Foundation and Magnifico playing on his visi-sonor instrument, and from everything we saw, it seems like the good guys won out.

But we don't actually get any closure there. The last thing we see is Bayta/the Mule collapsing in telepathic defeat. Great. Is she dead? Why did Gaal end up running away and jumping out of a window into her ship? Where is the Mule? Where does this story go next?

If the show follows the books here, the Mule is defeated. He goes down when he has a cognitive showdown with the leader of the Second Foundation. However, in the printed version, he isn't killed. He isn't even dethroned. For lack of a better word, he's mentally neutered. He stops antagonizing the Second Foundation and becomes a benevolent ruler before dying from his mutation at a young age. When we get to season 4, will the Mule still be hunting for the Second Foundation? Will she be mentally neutered and ruling the conquered Foundation with a feather-light fist? This is a spot where we definitely need some closure moving forward.

The other elephant in the room is the Second Foundation. Gaal Dornick and Hari Seldon developed the group on Ignis throughout season 3. They would pop in and out of hypersleep, teaching the fledgling mentalic community about the mathematical approach to predicting the future called psychohistory. Over decades, they slowly turned the Second Foundation into a mind-bending force to be reckoned with.

Here's the thing. The Second Foundation's job in the books isn't really to stop the Mule. Sure, they step in and shut him down when things get out of hand, but their purpose is much bigger. They are set up long before the Mule is a threat. Hari Seldon has them in place from the beginning of his plan to covertly watch over and guide the First Foundation.

This larger purpose has been touched on in the show. In episode 2, "Shadows in the Math," Hari showed Gaal his Prime Radiant projections for things that will happen after the Mule. But the Second Foundation's larger role in guiding the future of humanity is still downplayed in the show. Up until now, it's been all about preparing for and then stopping the Mule. Here's hoping we see the clandestine group step into the limelight in a wider capacity in season 4 — the same way it does in the later books.

I love the whole Brother Dawn, Brother Day, Brother Dusk concept as much as the next guy. It's a fun extra layer of the story (even if it's made up for the show). But at this point, the Galactic Empire has stuck around in this adaptation for much longer than it does in the books. By the time the Mule shows up in the second book, "Foundation and Empire," the Galactic Empire is in tatters. Trantor is being picked apart for its scrap metal and has large swaths of farmland where a bustling, urban, planet-sized city-center of 40 billion people once stood. Imperial power is broken, and its final strongholds are crumbling.

In the Apple TV+ show, this hasn't happened yet. Trantor is still alive and well. However, its downfall is ready to be set in motion as of the end of season 3. The shocking finale included a wild twist where Brother Dusk (Terrence Mann) becomes Brother Darkness (i.e. they're about to euthanize him). Facing his own mortality, he snaps, turning on everyone, blowing up his undecanted brothers, killing Brother Day in cold blood, and destroying Demerzel's (Laura Birn) body. This means, apart from Brother Darkness and a single clone of Brother Dawn (Cassian Bilton) over on New Terminus, the Genetic Dynasty no longer exists. Demerzel, the positronic mastermind behind the dynasty, is also no longer in the building (don't worry, though — she'll be back).

So, what's next? Empire is still kind of, well, there. Right? It hasn't fallen yet. Sure, the Mule destroyed its fleet of warships, and its leaders are gone. But it hasn't actually fallen yet. Hopefully, by season 4, we get some solid closure on the end of that chapter of human history — even as the next chapter of the Foundation takes its next leap forward.

There are a couple of key characters whom we need to meet soon — possibly as soon as "Foundation" season 4. The first is Golan Trevise. At first glance, Golan isn't important. He's just another Foundation councilman churning through the power politics of a growing galactic empire. However, Golan ends up being the pivotal character for the entire fourth and fifth books of the series due to his extraordinary natural sense of, wait for it, intuition. Asimov's last two novels follow Golan across a galaxy-spanning adventure that sets up the entire final stages of the "Foundation" story. Even better? Golan is the linchpin that brings everything together. We need him cast and on-screen soon!

The other person is Stor Gendibal. Stor becomes a young and restless leader of the Second Foundation long after the threat of the Mule is gone. He has ambition and wants to lead well, but he ends up unwittingly drawn into the larger narrative web of the story against his own will. Again, we need this guy in the mix ASAP.

There are a couple of other characters we will hopefully meet soon, too, like the elderly historian Janov Pelorat and his mentalic girlfriend Bliss. Really, Golan and Stor are the first two we need to get first, though. The rest of the upcoming cast of characters will fall into place after that.

The Second Foundation was fully rolled out in season 3. There were a few changes to the group compared to Asimov's books, but that is inevitable when adapting source material as sprawling and convoluted as this. Despite the differences, I'm really impressed with how they've handled the counterpoint to the First Foundation — especially in the area of mentalics. This is the tricky concept Asimov introduced where humans use their minds to influence and, occasionally, control others. The Second Foundation is the first iteration of this phenomenon, but there's another, bigger, better version of this concept coming soon: Gaia.

Gaia is more than a collection of mentally acute and capable individuals. It is a living and conscious planet full of them. Gaia is settled by humans (guided by robots) who develop their mentalic abilities far beyond the Second Foundation. They become a collective organism that shares a group consciousness so nuanced that it extends to the flora and fauna, too. Remember earlier when I mentioned that the changes the show made with the Mule? They also changed the character's backstory. In Asimov's books, the Mule is actually a mentalic from Gaia, and at one point, his fellow Gaians are even referred to as the Anti-Mules.

I won't give too much more away about Gaia here, because it really is a big deal in the story. What I'll say for now is that this living planet becomes an integral part of humanity's potential future. Unless the showrunners write Gaia out of the story or combine it with the Second Foundation or something, it can't be too far away from a reveal in the show, especially considering what we saw in the final moments of season 3 — which leads me to my last point.

Demerzel was physically destroyed in the season 3 finale. Guess what, though? No such thing happens in the books. In those, the narrative follows the Foundation, and Demerzel simply disappears from the storyline as the Galactic Empire collapses out of sight and out of mind. But that doesn't mean she's unimportant. The opposite, in fact: Demerzel is the key figure who brings everything together.

In Asimov's books, Demerzel is present on the Moon colony that we see in the fading moments of season 3. That is a really important place where Golan Trevize and company travel to in their quest to find Earth. There are some hella crazy revelations that take place once everyone gets there, too. Basically, Demerzel and the Moon are a Really. Big. Deal. They also help wrap up the story. Introducing them so early in the larger arc of the show is a bit confusing. It makes me wonder if they're going to do away with the element of surprise with the Moon colony and see more of it in season 4. Then again, now that they've hinted at it, maybe we won't see it again until the end of the show. Only time will tell.

"Foundation" season 3 is streaming, in its entirety, on Apple TV+.