Meisterwerke

Earlier, the position must have been something like this: (or bRg3, or wBg4 anywhere on the diagonal c8-g4)

From this, forward play is: 1. hg3 h2 2. Bh3 h1=N 3. g4 Ng3 4. b4 Nf1 5. Rg3 a6 6. Ref3 Ne3 7. b5 Nd1 8. Re3 ab5 9. Ref3 Qe3 10. Nd3 Nb2 11. Ne5 b4 12. Ng6 Qd3.

Now only the black queen, and the white knight can move to reach the problem position with a white knight added. If the knight is added on a white square, white has the move, but can't give mate. Therefore the knight must be added on a black square, and black has the move. The only black square on which the knight can be added to give black the opportunity for a #1 is e3, and black has a #1 with Qd4# then. This position is reached by continuing the forward play 13. Nh4 Qe3 14. Nf5 Qd3 15. Ne3 Qd4#.

Solution by Henrik Juel