Five hundred years after the establishment of the Foundation, the Mayor of Terminus, Harla Branno, is basking in a political glow, as her policies having been vindicated by the recent successful resolution of a Seldon Crisis.

Golan Trevize, a former officer of the Navy and now a member of Council, believes the Second Foundation, which is almost universally thought to be extinct, still exists and is controlling events.

Branno also believes that the Second Foundation still exists and is in control, but she cannot admit it publicly for political reasons, and treats that as a state secret, hence her alarm and her swift action.

As a cover, he is to be accompanied by Janov Pelorat, a professor of Ancient History and mythologist, who is interested in the location of Earth, the fabled original world of the human species.

At first, Gendibal's ideas are very badly received by the other Speakers, with Shandess alone supporting him, and he is threatened with expulsion, but the Speakers' resistance is overcome when Gendibal demonstrates that the brain of Sura Novi, a member of the Hamish, the rude people of farmers who inhabit and cultivate Trantor, shows a subtle change to her mind that would be far beyond the Second Foundation's capabilities to make, and could only have been made by a much more powerful entity, probably the "Anti-Mules".

They travel there and discover that Gaia is a "superorganism" where all things, both living and inanimate, participate in a larger group consciousness, while still retaining any individual awareness they might have.

"[3] Dave Langford reviewed Foundation's Edge for White Dwarf #39, and stated that "At 200,000 words, the sequel seems longer than the original series; endless pages of grey dialogue about the fate of the galaxy are on the whole boring, and the trilogy is weakened, not strengthened, by the addition.

For example, the trilogy's goal of peaceful Galactic Empire is now rejected, presumably because of fascist implications: this is all very Politically Correct but converts the first three books to pointless chronicles of misguided effort.