About the book (from Wikipedia):
Foundation and Earth is a science fiction novel by American writer Isaac Asimov, the fifth novel of the Foundation series and chronologically the last in the series. It was published in 1986, four years after the first sequel to the Foundation trilogy, which is titled Foundation’s Edge.
Several centuries after the events of Second Foundation, two citizens of the Foundation seek to find Earth, the legendary planet where humans are said to have originated. Even less is known about Earth than was the case in Foundation, when scholars still seem to know the location of ‘Sol’.
The story follows on from Foundation’s Edge, but can be read as a complete work in itself. (It does, however, give away most of the mysteries around which Foundation’s Edge is built.)