Black's king is stuck in the centre and White took advantage.
1.Rxc7! Qxc7 (1...Rxc7 loses to 2.Nxb5, followed by 3.Nxc7+ and then 4.d6, forking queen and bishop) 2.dxe6 fxe6 3.Nxe6 (this knight's a killer - White just needs to move the other knight to threaten Qh5 mate) 3...Qc6 4.N2d4 Qxe4 5.Ng7+ Kd8 6.f3 Black resigns. 7.Nde6+, picking up, the rook will follow.

Andrew Lewis vs. Richard Webb, Barbican 4NCL 3 vs. Wessex 1, Division 2