And now some intersections between our back rank patterns and the pin. Here Black can play RxQ, but White’s reply NxR+ is a nasty fork that wins the exchange when the smoke clears. So back off and assess the board. Your thinking about a position always should include attention to the enemy king’s position and any vulnerabilities in it. Here that means seeing that White’s king is trapped on h1 and ready to be mated if you can drop a heavy piece onto the back rank. You can't do that yet because your queen and rook are on the d-file, which White blocks with a protected pawn on d3. But don’t stop there; notice that this means the d3 pawn is pinned, since if it moves off of the d-file Black has Qd1+ and then White only can offer the useless interposition Qf1 (resulting in QxQ# for Black). The natural way to exploit a pinned pawn is by taking something it protects, so Black plays QxN.
Or does he? Before plunging forward with a move like QxN, one must take due care to ensure that the position it leaves behind is safe. The good news after QxN is that Black threatens mate with Qe1, so White has no time to take the rook that has been left loose on e6; rather, he has to evacuate his queen, as it is now hanging. But notice that since White is not himself in check, he has the liberty to give checks of his own—and with a loose rook lying around you have to make sure White’s checks won’t amount to anything. Let’s see: 1. …QxN; 2. Qh8+, Kd7; 3. Qg7+, Kc8; 4. Qf8+, Kb7; 5. Qe7+, Kb6—and now Black’s king is safe. White has at last made it possible for himself to play QxR, but it’s no help because it’s not a check and thus gives Black time to mate on the spot with Qe1. So QxN works here for Black. Realize, though, that all this is a little delicate. If Black plays 4. …Kc7 instead of Kb7, he blunders away the game: now White’s 5. QxR+ is a check that leaves Black no time for Qe1. Black does have the consolation of recapturing with KxQ, but since his rook is off the board White now is free to play d3xQ. All the pieces are gone.