The open diagonal running toward Black’s king cries out for consideration of a bishop check: 1. Bc4+. What are Black’s options in reply?

(a) He can capture the bishop with his queen, which is then lost to RxQ. An ugly outcome for Black, but it turns out to be the best he can do.

(b) Black can move his king to h8. Now you should see that you have half of Greco’s mate in place; if the h-file were opened, White could mate there with his queen. White's only resource for opening the line is his knight, which can't give check—but it can threaten mate, suggesting an idea we saw in skeletal form a moment ago. 2. Ng5 threatens Qh7#, and so forces h7-h6; now White plays 3. Qg6, moving his queen into the hole created by the advance of the h-pawn. He still is threatening Qh7#. Black extinguishes that idea with h6xN; but then White moves his queen over and back to h5 and mates there. It's a nice little study in the art of opening a file.

(c) Black might instead reply to Bc4 by interposing his rook at f7. In that case White plays QxR+, establishing a battery of queen and bishop and mating on g8 next move. Since White's capture gives check, Black has no time to strengthen his back rank (say, by moving his knight out of the way of the rook on a8).