30...........d2+
A) 31.Rxd2 Nxd2
32.Kxd2 Rxf2+
33.Kd1 Qxe4 White Queen falls
34.Kxf2

B) 31.Ke1 Rxf2
32.Qxg6 Nxe3#

White threatens 31.N(Q)xf5.

The white can can only move along the first rank and the white queen is defenseless. This suggests 30... Rxb5, threatening 31... Rb1# and 31... Qxe4:

A) 31.Nxb5 Qxe4 - + [Q+P vs R].

B) 31.Qxg6 Rb1#.

C) 31.Nc6+ Qxc6 (or 31... bxc6 32.Qxc4 Rg1+ 33.Kd2 Rxh1 34.Rb2+ Ka8 35.Qa6 Rb8 - +) 32.Qxc6 Rb1#.

<30 ... Rxb5>

31 Qxg6 Rb1#

31 Nc6+ Qxc6 (Now threatening Rb1# and Qxh1# if the queen moves)

31 Nxb5/Kf1 Qxe4 (Now threatening Qxh1#)

31 f3/f4 Qxg3+
32 any move Rb1#

~~~

FWIW: I thought 30...d2+ was sufficient

First, the simple and flawed "mainline":

<30...d2+> 31.Rxd2 Nxd2 32.Kxd2 Rxf2+ 33.Kd3 Rd2+

Or the other option

<31.Kd1> 31...Nxe3+ 32.Qxe3 Qg4+ 33.Kxd2 Rxd4+ 34.Kc3 Rf3

but the simple 33.f3 refutes this :(

Instead White could have played 29. a4 = equalizing, or, failing that, 30. Qxc4 Rxf3 to putting up more resistance.

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and white is now a pawn up>

The big hint for me was that the rook was double attacked and pinning the queen so I figured that that was the piece that had to be looked at first.

I also liked <gofer>'s 31 f3?? Qxg3+ mate next move line.

click for larger view

White cannot cope with the double threat of Rb1# and Qxe4, he loses at least his queen for a rook (31.Nxb5 Qxe4) or a rook for nothing (31.f3 Qxe4 32.fxe4 Rb1+ 33.Kf2 Rxh1).