The idea behind this move is to bring the Queen to the kingside and temporarily prevent Black from initiating exchanges by 12....Nd7. With the Queen on the kingside, ready for attack, White threatens an improved version of Torre's sacrifice with Rxe7 and Bxf6, disrupting Black's kingside pawns and exposing his King to direct attack. The Queen and Bishop combine to put indirect pressure on the Bishop at e7, so Black must take steps to reinforce it.
Black has a number of alternatives here, but this seems the best way of meeting the threat of 13.Rxe7. For example:
1) 12....h6?! 13.Rd3 (13.Rxe7!? +=) 13....hxg5 (13....d5 14.Bxh6!) 14.Nxg5 Re8 15.Rh3 Nh5 16.Rxe7! g6 17.Rxe8+ Qxe8 18.Re3?! (18.g4! ±) 18....Qf8 19.Nd5 Qg7 20.Nxc7 += Browne-Taylor, BCCC 1993.
2) 12....Qd7 13.Rxe7!? (13.Rd3 Rfe8 14.Rxe7 Nxe7 15.Bxf6 Ng6 16.Qd4 c5 17.Qxc5 dxc5 18.Rxd7 gxf6 19.Rxb7 Nf4 =+)13....Nxe7 14.Bxf6 gxf6 (14....Ng6 15.Ne5! +=) 15.Ne4 Qf5! 16.Nd4 Qe5 (16....Qg6?! 17.Rd3! Kh8 18.Nxf6 ±) 17.Nxf6+ (17.Rd3!? Kg7 18.Rh3 h5 19.Nf3 Nf5 20.Nxe5 Nxh4 21.Nd7 is unclear) 17...Kg7 18.Nd7 (18.Qxh7+ Kxf6 -+) 18...Ng6 19.Qg4 Qf4+! 20.Qxf4 Nxf4 21.Nxf8 Rxf8 22.g3 Ne6 =
White could venture Torre's sacrifice 13.Rxe7!? when Black must defend very accurately. It appears, though, that White only achieves a draw with best play on Black's part.
1) 13.....Qxe7? 14.Nd5 Nxd5! 15.Bxe7 Ndxe7 and White should win.
2) 13...Nxe7 14.Bxf6 gxf6 15.Ne4 Ng6 16.Nxf6+ Kg7 17.Nxe8+ Qxe8 18.Qd4+ += and material is equal but Black's kingside pawn formation is shattered.
3) 13....Rxe7! (After this move, White can only gain a draw) 14.Bxf6 gxf6 15.Nd5 Re6 16.g4! Kh8 17.g5!? (Safer is 17.Nf4 Re8 18.Nh5 Re6 19.Nf4 =) 17...Ne5 18.Nxe5 fxe5 19.f4 (Not 19.Nf6 Rxf6 20.gxf6 Qg8 21.f4 e4 22.f5 Qg2 =+) 19...Rg6 20.Nf6 Rg7 21.Nh5 (21.fxe5 Qe7! =+) 21...Rg6 22.Nf6 Rg7 23.Nh5 =
Better appears to be 13...Qd7!, when White has no good forcing options:
1) 14.Rxe7!? Nxe7 15.Bxf6 Ng6 (15...gxf6 16.Ne4 Qf5 17.Nd4 Qg6 18.Nxf6+ Kg7 19.Nxe8+ Rxe8 20.Re1 +=) 16.Qd4 c5! (16...gxf6 17.Nd5 Re6 18.Nxf6+ Rxf6 19.Qxf6 Qe6 20.Qxe6 fxe6 21.Nd4 +=/=) 17.Qxc5 dxc5 18.Rxd7 gxf6 19.Rxb7 Nf4! 20.Rc7 Ne2+ 21.Nxe2 Rxe2 22.Rxc5 Rxf2 =+
2) 14.Rde1 h6! (14...d5 15.Bxf6 Bxf6 16.Qg4! Re6 17.Rxe6 fxe6 18.Qxe6+ Qxe6 19.Rxe6 Bxc3! 20.bxc3 Rf8 21.Kd2 h6 22.Kd3 Kf7 23.Re1 g5 24.c4! g4 25.Ne5+ Nxe5+ 26.Rxe5 dxc4+ 27.Kxc4 =) 15.Bxf6 Bxf6 16.Qh3 Red8 17.Qxd7 Rxd7 18.Nd5 Bd4 19.Nxd4 Nxd4 20.Ra3 Kf8 =+
3) 14.h3!? (Since White can force nothing he may as well delay) 14...Bd8 (14...h6?! 15.Rxe7 Nxe7 16.Bxf6 Ng6 17.Qd4 c5 18.Qd2! gxf6 19.Qxh6 is unclear) 15.Rxe8+ Nxe8 16.Nd5 h6 17.Bxd8 Qxd8 18.Re1 Qxh4 19.Nxh4 Nd4 and Black appears to be escaping the bind with an advantage.
Not as clear was 14...Bxg5 15.Nxg5 h6 16.Rxe8+ Qxe8 17.Nxc7!? (Better perhaps 17.Ne4 which keeps up the pressure) 17....hxg5 18.Qg4 Nf6 19.Qxg5 Qf8 20.Nxa8 Qxa8 21.Rd3 and White has chances.
Less clear but probably better was 15...Nde5. For example: 16.Qg3 Kh8 17.h4 Nxf3 18.Rxf3 Bf8 19.h5 Ne5 20.Bxe5 Rxe5 21.h6 g6 22.Nxf6 Bxh6+ 23.Kb1 Qe7 24.a3 Re1! 25.Rxe1 Qxe1+ 26.Ka2 Qe6+ 27.Kb1 Bg7 28.Qh4 h6 29.g4 and White still has some pressure but Black should be winning.
Black has defended superbly up to this point, and this lapse should have thrown away any hope of maintaining his pawn advantage into the ending. White might have achieved equality here with best play, however. For example: 16...Qd7 17.Nd4 Nxd4 18.Rxd4 Bf8 19.Rh3 h6 20.Rg3 Nxd5 21.Qxd5+ Qf7 22.Bxh6 and White has regained the pawn.
White regains his pawn with a clear edge after the simple 17.Rxe8 Qxe8 18.Qxe8 Rxe8 19.Nxc7. Now it is Black who retains the edge despite White's pressure.
Not the most attractive option, since it opens up the a-file (which proves troublesome for White). But not much better was 19.f4 Nxd5 20.Rxd5 c6 21.Rd1 Nc4 =+.
Black seizes the initiative after this move, but also allows great complications, which is precisely what White would like. A safer course of action was 20...g6 21.Qe2 Nf7 though White will have pressure on the kingside still. One must admire Black's courage here, though.
Worth a try was 22.Nxf6+!? Qxf6 23.Qxh7+ Kxh7 24.exf6 Ra1+ 25.Kd2 Bh6+ 26.Ke2 Rxd1 27.Kxd1 Bg5 28.f7 Be7 29.Nf3 Kg7 =+, though White should lose the ending of Bishop versus Knight even if Black's extra pawn is doubled.
Black begins to go wrong in the complications. Winning was 27...Qa4! 28.e6!? Ra1+ 29.Kd2 Rxd1+ 30.Kxd1 Qxh4 31.Ng8 Qg4+ 32.Kc1 Qxe6 33.Kb1 Kf7 34.Qxh7+ Bg7 and White has nothing for his piece. The position is now very unclear and either player could assume the advantage with the slightest slip by his opponent.
White's Knight at e7 is still off limits: 28...Kxe7? 29.exd6+! cxd6 30.Qxh7+ with a winning attack since the Bishop must fall.
And if here 29...Kxe7? 30.Qf6+ Kd7 and White can choose between winning material by 31.Qf7+ or continuing the attack with 31.e6+!
Black cannot simplify with 33...Qe1+ 34.Kf3 Qxe5 35.Qxf8+!! Kxf8 36.Nhxg6+! hxg6 37.Nxg6+ Kg7 38.Nxe5 dxe5 when it is likely White who has the edge in the ending.
The losing move. After 34.Kf3! the game was still quite balanced.