I was just about to write how easy this one was, when I noticed that the "brilliant" line I had come up with contained a flaw.

I originally wanted to play 20...Nxb4 21 Rxa5 Nc2+ 22 Ke2 Bc4#, except that it ISN'T mate, white has 23 Kf3.

Next I decided to try 20...Nxc3 thinking that after 21 Rxa5 Rd1# would be mate (and it is this time), but, of course, white isn't compelled to play 21 Rxa5, and 21 Qxa5 seems like a much better choice.

I think I have finally settled on

20...Rd1+

White has three legal moves

- 21 Rxd1
- 21 Kxd1
- 21 Ke2

none of them good. After

21 Rxd1 Nxb4 22 cxb4 Qxb4+ 23 Ke2 (23 Rd2 Rd8 is ugly) 23...Bc4+ 24 Kf3 g4#.

and white has been checkmated. On

21 Kxd1 or 21 Ke2

black gets to play

21...Nxc3+

followed by the capture of the queen.

This "Easy" position took me entirely too much time, mostly because of some of the tempting candidates at move 20.

I immediately noticed that both Queens were under attack, and thus were likely to be the subject of the puzzle. I concentrated on trying to win the opposing Queen. I also realized that the direct capture of the Queen with 20...♘xb4 couldn't produce anything after 21. ♖xa5 ♘c2+ 22. ♔e2. The first move I seriously considered was 20...♖d1+, noting that 21. ♖xd1 prevents recapture of the Queen. But 21. ♔xd1 caused problems, so I moved on.

The next move I considered was 20...♕d5, creating a checkmate threat while attacking the Queen. But I quickly noticed that 21. ♕d4 forces a Queen trade with no significant advantage for Black.

Rybka 3 says in fact taking with the King drops the Rook and dark square Bishop to boot!

Evading with 21 Ke2 drops the Rook, so in fact I was wrong, White does take with the Rook and drops the Queen:

21 Rxd1 Nxb4

the important point here being that White cannot take back the Knight without fatally exposing his King; so the position is indeed resignable.

22 cxb4? Qxb4+
23 Rd2 Rd8

click for larger view

I am guessing you mean that the winning exchange would be something like: 24.Bxc4 Rxh1, right?

click for larger view

Except I didn't see it and was seduced by the dark side of the force wth the same Nxb4 line that most others fantasised over.

Too messy for an unplugged diagram, except perhaps this one:

click for larger view

Ironically I went back to the very first move that jumped out at me, and after a second look it works:

20 ...Rd1+

a) Now if white plays 21. Rxd1 then black plays 21 ...Nxb4; 22. cxb4 Qxb4+ Black emerges with a queen and a pawn for a knight and a rook, but black also looks to have persistent threats against the white king and white has to be careful with the rook. For instance playing 23. Rd2 leads to the nasty 23 ...Rd8. But if white plays 23. Ke2 (what other choice is there), then the white king looks to be harassed for some time to come from the black pieces. I haven't worked this line out exactly, but with white's undevelopment and black's material advantage, then it doesn't look good for white.

b) Or white can play 21. Ke2 or 21. Kxd1. In either case black has 21 ...Nxc3+, which conveniently removes the white queen's pawn defender. White should respond with 22. Qxc3 followed by 22 ...Qxc3. So again, with best play white loses a queen and a pawn and gains a rook and a knight. Once more things do not look good for white - down material with an exposed king.

My engine-based evaluation method rates this puzzle as a difficult Tue or easy Wed.

20...Qxb4
21 cxb4 Nxb4

And was hoping that improved the position for black. I knew there was a possible fork, but I did not think it through.

If 20... Nxc3 White won't play 21.Rxa5 because of 21... Rd1#, but 21.Qxa5 winning. However, this line suggests 20... Rd1+:

A) 21.Rxd1 Nxb4 22.cxb4 Qxb4+ 23.Ke2 (23.Rd2 Rd8) Bc4+ with Q+P vs R+N and a winning attack.

B) 21.Kxd1 Nxc3+ 22.Qxc3 Qxc3 with Q+P vs R+N and a winning attack.

C) 21.Ke2 Nxc3+ 22.Qxc3 Qxc3 23.Rxd1 Bc4+ 24.Kf3 Qf6+ 25.Kg4 (25.Ke4 Re8#) Be6+ 26.Kh5 Qg6#.