2024/04/20: "Variations On A Theme By Queen+Knight"

White to move.

The White Queen can check on h7, protected by the Bishop.

White's Rook is en prise.

Black has dark square weaknesses.  And the e5 pawn controls both d6 and f6 escape squares.

1. Qh7+ Kf8  2. Qh8+ Ke7  3. Nc8+ fails due to 3. ... Rxc8  4. Rxc8?? Qxg2#

So it looks like every move must be a check.

We can re-order the move sequence and insert an Intermezzo:  1. Qh7+ Kf8  2. Rc8+ Rxc8  3. Qh8+ Ke7  4. Nxc8#.

There's another possibility:  2. ... Ke7  3. Qe8#

I think the solution will be the first line since it's one move longer and involves checkmate with the Knight, a lesser piece than the Queen.

No, I miscalculated:  in the 2nd line, my Queen is still on h7, not h8.

So I have to play 1. Rc8+ first.

.

The key was seeing that 1. Qh7+ failed due to the King escaping to e7 without the Knight check.  1. Rc8+ guaranteed that 4. Nxc8 would be checkmate because the Rook no longer guards c8 and the Queen controls the entire back rank.  And don't overlook the mighty pawn on e5.

My error was due to the fact that I had calculated what I thought was a winning line, found an alternate defense for the opponent, but didn't go back to the beginning to make sure my idea still worked.

You might have noticed that last week's theme was Bishop-dominated and this week has been the Queen & Knight show.  Solvers are forewarned for tomorrow [no guarantees, though].