You're White in this position and considering playing Rab1. What moves might Black make in reply? His queen's attacked, so the natural moves seem to be Qxa4, Qc3 or Qa2. Anything else?

Veselin Topalov certainly didn't think so when he decided to play 23.Rab1 against Vladimir Kramnik in the current Linares tournament. He must have been shocked when his opponent whipped out 23...Bg4!! in reply. The first point is that 24.Nxg4 Nxg4+ 25.Qxg4 Qxc2 is good for Black, whose queen is very active. The next point is that 24.Nxg4 Nxg4+ 25.Kg1 allows either 25...Bxf2+ or, even better, 25...Ngxf2! 26.Rxb3 Nxh3+ 27.Kh2 Nf4+ forcing mate. Finally, 24.f3 Nxf3+! 25.Bxf3 Bxh3 leads to a winning position for Black.

One mark of a great tactician is the willingness even to consider moves such as 23...Bg4 - whether as Black, after 23.Rab1, or as White in thinking about the move. Such moves turn up with surprising frequency in Kramnik's games, which is what makes him one of the most exciting players alive today. Here are the full moves of the game.

White: Veselin Topalov

Black: Vladimir Kramnik

1 d4 d5 18 Nc2 Qxb2

2 c4 c6 19 Nd1 Qb3

3 Nf3 Nf6 20 Nde3 N7e5

4 Nc3 e6 21 h3 Be6

5 g3 Nbd7 22 Kh2 Rh6

6 Bg2 dxc4 23 Rab1 Bg4

7 a4 Be7 24 Nxg4 Nxg4+

8 0-0 0-0 25 Qxg4 Qxc2

9 e4 e5 26 Qg5 Nxf2

10 dxe5 Ng4 27 Rxf2 Qxf2

11 Bf4 Qa5 28 Rf1 Qd4

12 e6 fxe6 29 Be5 Qd7

13 Qe2 Nge5 30 Qc1 Qe6

14 Nd4 Nd3 31 Bxg7 Kxg7

15 Nxe6 Rf6 32 Qg5+ Rg6

16 Bc7 Qb4 33 Qxc5 Qd6

17 Nd4 Bc5 White resigned