
As much as the Apple TV+ series Foundation is an adaptation of the famous Isaac Asimov book trilogy of the same name, much of the mythology of the series pulls from material outside of the main trilogy, including Asimov’s robot novels, as well as some of the Foundation prequel books. In the fourth episode of Season 3, “The Stress of Her Regard,” Foundation dives into a part of the planet Trantor that connects both to robots and one of Asimov’s biggest retcons.
Basically, this season has reintroduced the concept of the Mycogen sector into the canon of the TV version of Foundation. And, this location doesn’t really originate in the 1950s novel trilogy, but instead comes from the 1988 prequel, Prelude to Foundation. Here’s how the newest Foundation episode reboots and redefines the Mycogen sector, and what it might mean for the series going forward.
Spoilers ahead.

Just as Asimov linked his Foundation books to his Robot books through the character of Eto Demerzel/ R. Daneel Olivaw, the TV version of Foundation has expanded its robot lore through various revelations from Demerzel (Laura Birn) in every single season. The big change in this season has been the revelation that an ancient religion of robot-worshipers called “The Inheritance” still dwells in the Mycogen sector, deep in Trantor.
In Episode 4, “The Stress of Her Regard,” the current Brother Day (Lee Pace) questions the AI memory of Cleon the First, and learns that back then, the very first Cleon went to Mycogen specifically to retrieve ancient robot tools, which Demerzel required for maintenance. Because Day’s lover, Song (Yootha Wong-Loi-Sing), is a believer in The Inheritance, Day hopes to find her there.
But the concept of an ancient society existing, somewhat hidden on Trantor, comes from Asimov’s Prelude to Foundation, a book that did a ton of work in recontextualizing Hari Seldon as a younger man, as well as creating the blueprints from Cleon and Demerzel, which more or less represent their roles on the show. In Prelude to Foundation, the Mycogen sector (or Mycogen district) is a place that Hari and his companion, Dors Venabili, flee to while on the run from the Empire. And, in an interesting twist, the character of Dors — who is one of Asimov’s more memorable female heroes — is actually, secretly, a robot.

There’s no direct analog for Dors in the TV version of Foundation. At least not yet. By the end of “The Stress of Her Regard,” Brother Day is headed into the Mycogen sector, trying to evade the Empire that, in theory, he is supposed to rule. And, he’s going there, not with a robot companion, but in search of a companion who loves robots.
So, if you squint, the latest twist in Foundation, the TV show, is an incredible remix of Asimov’s 1988 Foundation prequel novel. Much of the plot of Foundation Season 3 is focused on the machinations of the telepathic mutant known as the Mule (Pilou Asbæk), and those events are derived from the second half of the second book, Foundation and Empire (1952), as well as aspects of the third book, Second Foundation (1953). But all twists with Demerzel, Brother Day, and the descent into the Mycogen sector derive from a prequel novel that Asimov wrote over three decades after the original books were first published.
The premise of Foundation is inherently connected to a massive time scale; so far, we’ve covered about 300 years in three seasons. But, art imitates life, too, because the specifics for the latest Foundation twist also took several decades of waiting to fully manifest. Not all sci-fi epics are perfectly planned out in advance, and today, the retcons that Asimov made in the 1980s have enabled Foundation to deepen its canon and make the twisty journey of its characters even more compelling.