Chess/Puzzles/Directmates/Two-move 1/Solution

The solution is: 1. Qa2

If 1... Nc8... 2. d8=N#

Other attempts

 * The move 1. Qb3+ fails because the line 1...Nb5 2. Qxb5+ Kxa8 is mate in three, not two.
 * Likewise 1. Qb8+ fails to Kc6 2. Qb6+ Kxd7
 * And 1. c8=Q+ Nxc8 2. dxc8=Q+ Ka7 3. Qf7# is also one move too slow.