Find the decisive blow (difficulty 1215)

87654321 abcdefgh

White to move

Show solution
87654321 abcdefgh
  1. e4–d5 key move
  2. e7–f7
  3. e1–c3

What makes it

Mate is forced in six. The blow comes from a discovered attack — one piece moves, another fires. It calculates 11 plies deep.