Retract and mate

White retracts one half-move and mates in one. That is, undo a stupid mistake by White (I'm pretty sure it's a draw here, but I'm not a chess problem master so I'm not sure) and show that you're better by showing the correct move to mate immediately. Of course, the position after you retract a move must be a legal position (although not necessarily sound).

FEN: rb1Q4/kp6/p3K3/8/8/8/8/8

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EDIT: I thought I had it, but it was wrong.

White retracts 1. c7xd8=Q and plays 1. c8=N#. The Black piece on d8 is a bishop. Black had previously underpromoted to reach this position.

Very nice!

Correct solution. Now how many of you thought of retracting a queen move and doing another queen move...

Not many, since all the possible checks are blockable or suicidal.

No; since White is to retract, in the forward play Black has the move. So it's Black's turn. If it's White's turn, I also identified that mate in 3.

Oh thanks. I didn't know whose move it was.

Well, if White can retract then it means White has the last move, and so Black has the next move. But I suppose that wasn't clear enough, so yeah.