Frederic Friedel writes "Here's a nice little chess puzzle I got from Grandmaster John Nunn many years ago. It looks incredibly simple, but even the strongest players in world have been stumped by it. The problem can be stated in one simple line: A game begins with 1.e4 and ends in the fifth move with knight takes rook mate. What are the moves? If you want to read a couple of stories on it, go to Chessbase. There is a very special prize to be won if you are able to solve it -- a book signed by some of the world's top chess players, testifying that the winner is The Greatest. "
Update: 12/25 11:50 by michael : Well, I thought I figured it out, but I was wrong.
2. a4 b4
3. a1-a3 c2
4. a3-d3 b4
5. g7-e2 d3++
Just to clear up some confusion below, the condition is simply that a knight makes the last move of the game, which is a capture of a rook on move five (either color), and this results in checkmate for the other king. Either the knight or some other piece could be giving the check. One poster below reasons that black would be the one giving the checkmate - this is very sound reasoning. :) You just have to think outside the box.