This position is more advanced than the others we have seen in this chapter because it requires you to keep track of some variations. At a glance you should see that Black’s knight is about to get taken; you also should see the concentration of Black’s forces against the White king. Black’s bishop seals off b1 and c2, and his knight and rook form the kernel of a discovery—Nb3+ or Ne2+, almost mating by giving check with the knight and sealing off the king’s remaining flight squares with the rook. The mate is thwarted by White’s queen on a4, which guards b3, and by the bishop on f3, which protects e2. Focus on the impediment to Nb3+: threaten the White queen, and see if the threat leads either to its capture or to the abandonment of its defensive duties. Black has one way to so attack it without fouling up his mate threat. He plays the flush attack Qa5. Of course this leaves Black's queen en prise; he hopes White will take it, since Nb3# then follows. But in reply to a mere attack there typically is more than one possible move, so think carefully about what else White might do with his queen. Look for another square where it could keep doing the same thing: someplace safe where it would continue to guard b3. Answer: d1. So imagine White’s queen there and ask what comes next. Think in checks. Black can go ahead with Nb3+, and allow White to play QxN; then Black brings in his queen from its new position with Qd2#, putting it next to White’s king with protection from the rook on d8—a classic queen-plus mate.
White has another option in reply to Qa5: he can play Bd1. Notice that this protects his queen and also adds another defender to b3. Keep thinking in checks. How many would Black have after White’s Bd1? Two, either of which win the game. Nb3+ forces White to capture on b3 with his queen or bishop; either way, Black has Qd2#. Or Black can reply to Bd1 with Ne2+, which requires White to capture with BxN. As before, Black then has Qd2#. So White’s best reply to Qa5 turns out to be abandonment of the queen in favor of a different attempt to forestall mate—the simple e3xN, removing Black’s knight. In addition to winning White’s queen Black still has an eventual mate, but now it takes considerably longer as he has to chase White’s king around—perhaps all the way over to the h-file—with his queen, bishop, and rook.
This position illustrates one of our recurring themes in this section: when you attack the defender of a mating square, the dividends can be very great; but analysis also can be a good deal more complicated than it would be if you were working just with checks and captures, because your opponent has a wider choice of replies. You have to think hard about where the attacked piece might be moved and how you might follow up, and about what captures or attacks of his own he might be able to spring.