Dmitry Kryakvin v Evgeni Kulijin, Russian team championship 2008. Experts like to make sacrificial attacks leading to checkmate, and when this happens there is often a critical moment when only a precise selection can prove that the attack is sound. Here White (to play) has sacrificed a rook, and he now faces a plausible multiple choice. Should he go Nxf6+, Bxf6, Rxd1, Qg3, Qh4 or Qh6? All look interesting, but computer analysis shows that only one of them convincingly works. Exact calculation is needed, yet the decider is based on a checkmating pattern which often occurs in practical play and which any strong or improving amateur needs to know. Can you spot the right winning move?