Foundation's Edge | Isaac Asimov

It is 498 years since the two Foundations came into existence – half-way through the Interregnum planned by Hari Seldon.
The Second Foundation has once more successfully concealed its existence so that the laws of psychohistory can operate to usher in a new Empire ruled by the mental sciences.The Second Foundation is thought to be extinct…except by Councilman Golan Trevize.
Trevize fears that the mysterious Second Foundation will bid for power once a new Galactic Empire is established.
To prevent Trevize spreading alarm‚ the Mayor of Terminus exiles him to the abandoned ruins of Trantor.Accompanying Trevize is Janov Pelorat‚ Professor of Ancient History at the University of Terminus.
Pelorat hopes to find on Trantor a clue to the location of the planet that gave birth to the human race.
His belief in the existence of Earth is considered as far-fetched as Trevize's belief that the Second Foundation endures.
But the truths discovered by both of them on Trantor are far stranger than they could have guessed.