Find the decisive blow (difficulty 1395)

87654321 abcdefgh

White to move

Show solution
87654321 abcdefgh
  1. d4–f5 key move
  2. g7–h7
  3. f5–e7

What makes it

A knight move forces mate in eight. It is a discovered attack: the moving piece clears the way for the one behind it. It calculates 15 plies deep.