Find the decisive blow (difficulty 1005)

87654321 abcdefgh

White to move

Show solution
87654321 abcdefgh
  1. a2–a8 key move
  2. b8–a8
  3. e3–a7

What makes it

A rook move and a 5-point investment: mate in two. At 1005, no gift. A Chess960 setup puts the pieces on unfamiliar lines, and the tactic rides on exactly that.