Find the decisive blow (difficulty 1530)

12345678 hgfedcba

Black to move

Show solution
12345678 hgfedcba
  1. b6–b1 key move
  2. h3–g4
  3. f5–g4

What makes it

A queen move forces mate in 18. 35 half-moves of forced play. Difficulty 1530: brutal to see over the board.