Earth, at this time, is seen by the rest of the Galactic empire as a rebellious planet - it has, in fact, rebelled 3 times - and the inhabitants are discriminated against. Earth is also radioactive, although the cause is never given. The prequels elaborate on this point.
The religious fanatics who rule Earth have created a supervirus which they plan to use to kill or subjugate the rest the empire. Schwartz, along with some companions, is narrowly able to stop their plan.
Plot Summary
While walking down the street, Joseph Schwartz is the unwitting victim of a nearby nuclear lab accident which propels him into the year 12,411 AD. Due to changes in spoken language, he is unable to communicate with anyone. Mistaken for a mentally deficient person, he is put through an experimental procedure to increase his mental abilities. The procedure works, and also gives him telephatic abilities (including the ability to kill by thought). Themes
This book takes place in the same universe as the Foundation Series. There is even a reference to Trantor, later the planet where Hari Seldon would invent psychohistory. The theme of Earth being radioactive would show up again in Foundation and Earth.