Chess tactic for advanced players

The following complicated position arose in this year’s Tromso (NORWAY)  tournament between the Serbian grandmaster I.Ivanisevic and the Swedish master J.Sigeman.  White has strong attacking chances along the open h-file.  For this reason Black made a practical decision and chucked a pawn with  21…c4!? , trying to deflect White from his attack against the Black King and making room for the Knight to enter the fray via the c5-square.  If White now takes the pawn with his Knight , then Black exchanges Queens and eliminates the immediate danger.  The extra pawn that White would have is partially compensated by Black’s 2-Bishops.

Ivanisevic did not take the pawn.  Instead, looking deeply into the position, he found a powerful tactical idea that exposes the vulnerable position of the Black Queen.  Can you see it?  White to play and win!

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