Where does Black have the makings of a discovered attack? Actually in two places: on the c-file and on the h-file, where his knight masks his queen. Since we are focusing here on discoveries by bishops, start by working with the threat on the c-file. The rook on c8 is poised to take White’s queen if the bishop can be vacated from c5 in a forceful enough way. But where can it go? The first thing to consider is whether the unmasking piece can give check. That’s not possible here, both because the king is on a light square and because the pawn on f2 blocks the bishop’s path to the back rank. But when you see an obstruction like the f2 pawn, ask what you could do if it were gone. If the pawn weren’t there, Black could play Bg1. Does that qualify as interesting? It should, for then the position begins to look a lot like one we saw a few frames ago; the bishop would be attacking a square adjacent to White’s king at which his queen also would be aimed.

An idea thus emerges: if Black could get his queen aimed at h2 and get the f2 pawn out of the way, then Bg1 would threaten mate and be an effective discovered attack. The Black queen’s path is blocked by the Black knight on h5, but the knight can evacuate its square with check: NxB+. If White replies f2xN (the h-pawn can't be used because it is now pinned), now Bg1 is possible and threatens both Qxh2# and RxQ.

By the way, notice that White can reply to Bg1 with Bc4, limiting his immediate losses to a piece. White’s queen then protects h2 against a mating attack, since the White pawn and piece on the second rank suddenly are both gone. After Black plays RxBc4, White slides the queen over to e2, where it is safe and still foils the mate threat.

In a later chapter we will study knight discoveries like the one that unmasked the Black queen’s attack on h2, but already you can see how the train of thought might have started there just as easily: the knight in front of Black’s queen can move out of the way with check (NxB+). Black imagines the board as it would look after the recapture f2xN, and recognizes the same sort of idea we saw earlier: his bishop can unmask an attack against White’s queen, and at the same time add a second attack on the pawn in front of White’s king by moving to g1.