agb2002: Black is one pawn down.
White threatens Qxg7#, Rxg7+, Qxa6, etc.
Black has Bf3+, Rxh2+, Ra7, Bg4 and Bg6.
The obvious 42... Bf3+ 43.Bxf3 (43.Rg2 Rf1#) 43... Qxf3+ 44.Qxf3 Rxf3 45.Rg3 leads to an inferior endgame.
-----
The rook sacrifice on h2 only seems to achieve a draw, 42... Rxh2+ 43.Kxh2 Qf2+:
A) 44.Rg2 Qxh4+ 45.Kg1 Qe1+, perpetual.
B) 44.Bg2 Qf4+ 45.Kh1 (45.Kh3 Bg4#) 45... Qxh4+ 46.Bh3 Qxh3#.
C) 44.Kh1 Qxh4+ 45.Kg2 Qg4+ 46.Kf2 (46.Kf1 Qe2#; 46.Kh1 Qh3#; 46.Kh2 Qh4+ 47.Kg2 Qg4+ repeats moves) 46... Qe2+ 47.Kg3 Qg4+, perpetual.
D) 44.Kh3 Qf5+
D.1) 45.Kh2 Qf2+ repeats moves.
D.2) 45.Kg2(3) Qg4+ as in C.
D.3) 45.Rg4 Bxg4+ 46.Kg2 (46.Kh2 Qf2+ 47.Kh1 exd5 wins; 46.Kg3 exd5 47.Qxa6? Qf3+ 48.Kh2 Qf2+ 49.Kh1 Bf3#) 46... Qxd5+ 47.Qxd5 exd5 wins a piece.
-----
The decoy move looks far stronger, 42... Ra7:
A) 43.Qxa7 Bf3+ 44.Bxf3 Qxf3+ 45.Rg2 Rf1#.
B) 43.Rxg7+ Kf8 (43... Kh8 44.Rh7+ Kg8 45.Rg7+ repeats moves) 44.Qb8+ Kxg7 45.Qxa7+ Rf7 46.Qa8 Rf1+ 47.Kg2 Rg1#.
C) 43.Qc8+ Kh7 44.Qxe6 Bf3+ and mate in two.
-----
An interesting resource is 42... Bg6 (42... Bg4 43.Qb8+ Kh7 44.Qg3 Qxg3 45.Rxg3 exd5 46.Rxg4):
A) 43.Rxg6 Rf1+ and mate next.
B) 43.Bxe6+ Qxe6 44.Qxa6 Qe4+ and mate next.
C) 43.Qc8+ Kh7 (43... Rf8 44.Qxe6+) and White is defenseless against the double threat Be4+ and exd5.
D) 43.Qb8+ Kh7 44.Qe5 (44.Qg3 Be4+ 45.Bxe4 Qxe4+ wins decisive material) 44... Qxe5 45.dxe5 exd5 wins a piece.
E) 43.Bg2 Rxg2
E.1) 44.Rxg2 Qe1+ 45.Rg1 Be4+ wins decisive material.
E.2) 44.Qxg2 Be4 wins decisive material.
E.3) 44.Kxg2 Be4+ wins decisive material.
E.4) 44.Qc8+ Kh7 45.Kxg2 (45.Rxg2 Qe1+ 46.Rg1 Be4#) 45... Be4+ 46.Kf1 Ra8 is winning.
-----