Here's Black's helping move, Gd8:
Here's White's reply, Gd6 mate:
Here's Black's first move, Gh8+:
Note: Red is the indicator that the player to move is in check. White has three legal moves, Bf8, Bd8, and Ka7. The bishop moves simply prolong the game by one move. Let's assume White's reply is Ka7. Here's Black's final move, Gc8 mate:
Here's Black's first move, Bxg2+: White has one legal move, Kg1. Black then mates with Gh3: