Figure[White to move]

Here’s a variation on the current idea. Where does White have the kernel of a discovered attack? On the f-file. (The f7 bishop and f2 rook are separated more than is usual, but it’s no less important to see their relationship.) Having found the kernel, ask what the rook could do if the bishop were out of the way. It could attack Black’s rook on f8. That’s something, but on inspection of Black’s king there is more: the king has no flight squares and not many guards; so if White could play RxR it would be mate. This means that if the bishop vacates f7 it creates a discovered mating threat in RxR that functions like a discovered check: Black will have no choice but to fend off the threat to his king from White’s stationary piece, so White’s bishop—the unmasking piece—will get a free second move. White thus plays Bd5, attacking the queen.

Indeed, follow the possible resulting moves and you find that White need not be satisfied with the queen; mate soon follows no matter what Black does. If Black plays QxBd5, for example, he might seem to have created a defense against mate: if White plays RxR+, Black can play Qg8, blocking the check—yet then White mates with RxQ. If Black instead tries to extinguish the mate threat by replying to Bd5 with RxRf2, White can skip BxQ and just go straight for Black’s king with Qg8#; the queen gets cover from the bishop on d5. Black's "best" reply to Bd5 (it hardly matters) is Rd6-f6; all this does is throw a blocker onto the f-file. White's rook plows through it and Black soon runs out of stalling maneuvers.