Find the decisive blow (difficulty 1545)

12345678 hgfedcba

Black to move

Show solution
12345678 hgfedcba
  1. d5–f7 key move
  2. g1–g4
  3. h8–g6
  4. g4–e4
  5. b8–c6
  6. d1–a1
  7. d8–a8
  8. d4–d5

What makes it

The queen strikes, a 1-point investment, and the attack wins. A quiet move, soft as anything, and yet there is no reply. 8 half-moves of forced play.