RETROGRADE ANALYSIS CHESS PUZZLES

This type of chess puzzle was invented by Raymond Smullyan.
Before you can solve them, you need to work out 'what-happened-previously'.

You don't need to be an accomplished chess player to solve these puzzles.
All that's required is a knowledge of how the pieces move.
Smullyan's puzzles are studies in pure chess logic.

This one is relatively straight forward and I'll use it to give you
an idea of how to tackle Smullyan's puzzles.

WHITE TO MATE IN ONE MOVE  © Raymond Smullyan

A 'mate-in-one' should be dead easy, but we have a major problem here,
the Black King is invisible!  You'll need to locate it before you can mate it.
So where is it?  Well, it could be on almost any vacant square
that isn't next to the White King.  Right?  ........ Wrong!

Hint: Not forgetting that it's White's move, take a look at the positions of the Black Rook and the White King.  They could only get into this position,
relative to each other, with the involvement of the Black King.  But how?
Whether or not you can work it out unaided, you must click 'SOLUTION' to progress to a Smullyan Masterpiece.