When the First Foundation was conquered by a force Seldon had not foreseen – the overwhelming power of a single individual, a mutant called the Mule – the second Foundation was forced to reveal its existence and, infinitely worse, a portion of its power.
One man understood the shifting patterns of the inhabited cosmos. This was Hari Seldon, the last great scientist of the First Empire. The mathematics of psychohistory enabled Seldon to predict the collapse of the Empire and the onset of an era of chaos and war. To restore civilization in the shortest possible time, Seldon set up two Foundations.
The First was established on Terminus in the full daylight of publicity. But the Second, "at the other end of the galaxy", took shape behind a veil of total silence. Because the Second Foundation guards the laws of psychohistory, which are valid only so long as they remain secret.
So far the second Foundation's location, its most closely guarded secret of all, has been kept hidden. The Mule and the remnants of the First Foundation will do anything to discover it.