Find the decisive blow (difficulty 1125)

87654321 abcdefgh

White to move

Show solution
87654321 abcdefgh
  1. h5–g6 key move
  2. d8–h4
  3. h1–h4

What makes it

A pawn move forces mate in five. It calculates 9 plies deep. Difficulty 1125: a fair workout.