Two features of this position should jump out at you: the pin of White’s queen on the b-file and the kernel of a discovery for White along the g-file. (Black has a discovery prepared on the fourth rank, too, but it won't be our focus.) White has no target for the g1 rook once it is unmasked, but with the king on an adjacent file the question is not whether you can win material; it is whether you can threaten or achieve mate. White considers the check Nf7 and notices that the rook then seals off g7 and g8 as flight squares—and that the bishop on d3 seals off h7. Indeed, Nf7 would be mate were it not for the protection supplied to the square by Black’s rook on b7. So White plays 1. QxR, which removes the guard of f7 and incidentally extinguishes the pin of his queen. Now if Black plays BxQ, White mates with 2. Nf7.

You can view this position just as a way to win a rook, since Black dares not recapture White’s queen. That is the main thing to see in this position. But as an exercise it may be instructive to spend a couple of frames pushing this one farther. Find Black’s best alternative response and see where it leads. White’s mating threat depends on three players: his knight, rook, and bishop. Black looks to derail one of those pieces, and so plays 1. …Nf5, interposing his knight in front of the bishop and thus allowing his king a flight square on h7. Now White—working strictly with checks—plays 2. QxB+, which forces Black’s king to g7. We then come to the position in the next diagram....