I found this book at a used bookstore in Chicago after I had read the first part of Guralnick's Elvis biography, and after I learned he had written extensively about the blues.
This is one of Guralnick's forays into fiction, but the tale doesn't go too far from his nonfiction roots. In this book, a young white man from the Northeast (Guralnick, perhaps?) finds a stunning old bluesman in Mississippi and tries to make a national blues star out of him, kind of like when old bluesmen were "rediscovered" after the Rolling Stones and other white bands paid homage to them in the 1960s.
Of course, things do not go smoothly. The old bluesman is not in great health and does not have the mindset to bus from town to town playing one-nighters. Through the portrayal of the bluesman's home and other anecdotes -- like how his band's piano player disappears from a gig in Indianapolis, only to be found playing at a neighborhood dive -- the book seems to say that you can put someone on stage and call it the blues, but you can't really remove the blues from its environment. I get the feeling that Guralnick is channeling himself through the white promoter character, saying that the frustration with appreciating such great music is that you can't do it unless you come to it, not let it come to you.
The book is not so good that you should go to the ends of the Earth to find it, but if you liked Guralnick's nonfiction writing, Nighthawk Blues is worth picking up if you happen to see it.