In this position, all you need to know is that black made the last move. You must figure out exactly what that move was, and also what white's move was prior to it...nothing more. There is only one possibility. I assume the brains here will easily figure it out, but if after too long there isn't a solution, I will post it as cleverly revealed in the book's pages.
On a side note, if you like this kind of puzzle, and would like to read a good mystery/thriller with a snazzy chess game at it's core, read The Flander's Panel by Arturo Perez-Reverte.