In PRELUDE TO FOUNDATION, what happed in the many centuries before the events made famous in Asimov's other Foundation novels - hitherto only hinted at - is now revealed.
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.