Cyphelium: Rookpawn> 18. Nxf4 seems like a bad move to me. Black plays 18.- Nxd4! and now
A/ 19. Nxh5 Nxe2+ 20. Kf1 Nxe4 black has a piece and is easily winning.
B/ 19. Qd1 Qc5 20. Qxg4+ Kh8 and now threat is Nf3 double check:
B1 21. Qxh4?? Nf3+ wins the queen.
B2 21. Be3 Nxe4 is also really bad, for example white can't play 22. Qxh4 Nf3+ 23. gxf3 Qxe3+ 24. Kg2 Rg8+ 25. Kh3 Qxf3+ with mate.
B3 21. Bb2 Bf6 and white will fall apart because of all Nxe4, Bxb2 and Nf3/e2 double check threats that's just all over the place.
C/ 19. Qd3 might be best, but still...
C1 True, 19.- Qc5 now seems bad because of 20. Bxh7+ Kh8 21. Be3 Bf6 22. Rd1, but
C2 19.- Qe5! and black is on top. 20. Bxh7+ Kh8 (threat 21. -Qe1+ 22. Qf1 Bf2 mate) 21. Bb2 Ne2+ 22. Qxe2 Qxb2 with double threat against h7 and b2 is cheerless for white. Also, 20. Bb2 Nxe4 21. Qxd4 (21. Bxd4 Qxf4)Bf2+ 22. Qxf2 Qxb2 is pretty amusing: 22. Qe1 Qd4+ 23. Kf1 Nd2+ etc.