All records of Earth have been removed systematically from the libraries of Foundation worlds. Now Councilman Golan Trevize and Professor Janov Pelorat traverse the galaxy in search of humanity's ancestral planet. On worlds beyond the Foundation's influence, superstition and taboo shroud the subject of their quest. To name Earth is to utter an obscenity. Fortunately, the space travellers find allies - and Pelorat finds a lover named Bliss - among the telepaths of the planet Gaia.

As they near their destination, Bliss picks up thought waves of intelligent beings. What she cannot tell is whether or not those beings are human.