Black to play
Variation A ) Black cannot play the natural 18...Qxg4, as 19.Rxe8+ forces mate on the back rank.
Variation B ) And the tricky 18...Rxe2 does not work as a defense for Torre: White would simply grab the queen with 19.Qxd7 Rxe1+ and now 20.Nxe1 leaves White with a decisive material advantage.
So Black plays the only move that allows him to continue to protect the e8 square: 18...Qb5.
White to move
1. Suppose White played 19.b3 in response to 18...Qb5. What would Black's best move be?
2. Find White's best reply.
3. Try to find the best moves for both sides. How many moves ahead can you see?