This is a very pretty study. I didn't think the first move was all that hard to find- it was my first idea once I had absorbed the position, but it took me quite a while to prove it was the only win. How quickly can you do it?
1.Qg8+ Ke7 2.Qc8 Qb1 3.Qd7+ Kf6 4.Qd8+ Ke6 It's a draw.
White can't make any progress.
1.Qg4 Qb1 2.Qd7+ Kf8 3.d4 Qg6+ 4.Kh4 Qh6+
White can repeat perpetual check, but white can't win.
And why do moves like 1.Qg4 or 1.Qg8+ not win?
1.d4 Bc7 2.Qg4 Qb6 3.Qd7+ Kf8 4.Kh6 Bb8 5.Qc8+ Ke7 6.Qxb8 Qxc6+ 7.Kg5 Kd7 8.Qf8 f6+ 9.Qxf6 Qxf6+ 10.Kxf6 Kc7 11.Ke5 Kxb7 12.Kxd5 Kb6 13.Ke6 Kc7 14.d5 Kd8 15.Kd6 Kc8 16.Ke7 Kb7 17.d6 Ka6 18.d7 Ka5 19.d8=Q+ Kb4 20.Qc7 Kb3 21.Qc5 Kb2 22.Kd6 Kb1 23.Qc3 Ka2 24.Kc5 Kb1 25.Qd2 Ka1 26.Kb4 Kb1 27.Kb3 Ka1 28.Qb2#