Find the decisive blow (difficulty 1485)

87654321 abcdefgh

White to move

Show solution
87654321 abcdefgh
  1. d6–c7 key move
  2. d8–e7
  3. d3–d7

What makes it

A pawn move forces mate in nine. A piece slips off the line and the attack opens up behind it. 17 half-moves of forced play.