Author Bill Bryson (Robert Redford), successful and happily married, needs a new challenge in his life, and decides upon hiking the 2100-mile Appalachian Trail.
His wife Katherine (Emma Thompson) doesn't want him going alone, but his friends all decline his invitation. Finally an old traveling buddy, Steven Katz (Nick Nolte), hears about Bryson's trip and calls to invite himself along.
Katz is out of shape, a recovering alcoholic and just a bizarre individual, but fun and kind hearted. They enjoy being together again on an adventure, seeing magnificent views on the trail and meeting colorful characters along the way. Katz keeps telling Bryson he ought to write a book about it, and Bryson says he's not going to.
Even though they don't finish the entire trail (they seem to stop about halfway), the experience has benefited them and they return to their lives happy and satisfied.
Back at home in New Hampshire, Bryson goes through his accumulated mail and sees that Katz had been sending him humorous postcards all along their journey. He decides to write the book.