backrank: The position after Black's 23th move appears in Walter Korn's 'The Brilliant Touch in Chess'.
24. g4! is an ingenious preparatory move to the following combination. White sees that, after sacrificing on h7, he can't mate on the h-file, but he could if there stood a pawn on g5, supporting the white queen on h6 and depriving the black king on the potential flight square f6.
Black can't do much to prevent the white combination. He tries to deflect the Bc4 (which plays an important role in White's combinative play) from the diagonal b3-g8. His move 24. ... b5 eventually leads to the situation that after White winning the black queen, Black still remains in the possession of enough material for fighting on.
The alternative 24. ... Ra7 would have led to a similar, but even more drastic finish: 25. Nxh7 Rxh7 (Nxh7 26. g5 is even worse for Black) 26. g5 Qg7 (Qe7 27. Qxd4+ Qg7 28. Rxh7+ Nxh7 29. Qd8+ Qf8 30. Qxf8#; or Qd8 27. Qe5+ Rg7 28. Rxh7+ Nxh7 29. Rxh7+! Kxh7 30. Qh2#) 27. Qd6! [Chernev] with the deadly threat 28. Rxh7 (Qxh7 29. Qxf8# or Nxh7 29. Qd8+), against which 27. ... Rd7 fails to 28. Rxh7+ Nxh7 29. Rxh7+!.
But we shouldn't admire but the combination itself here. It is only the logical consequence of many fine preparatory moves, the first of which is 12. Ng5!, forcing Black to make the weakening move g6, so that White has a target for storming with his h-pawn. Black, in principle, defends well against that pawn storm. After hxg6, he retakes with the f-pawn (rather than with the h-pawn) to be able to defend the pawn h7 by heavy pieces along the 2nd rank.
16. Rh6! menaces Nxh7, but after Rd7 Black is temporarily safe. 18. Ne4 forces Qe5, because Black must let the white queen neither to f4 or g5. So White gains a tempo for storming with the f-pawn. 20. f5! is another very nice preparatory move, this time a pawn sacrifice, which opens the diagonal b3-g8 for the white bishop which will play a key role in the ensuing mating attack. After 23. Qf4 the position of the white pieces is ideal; he menaces to finish off Black by Qh4. Therefore, a5 is necessary to be able to defend by Ra7. If instead Bb7, White wins by 24. Qh4 (threatening Rxh7+) Qg7 25. Nxh7 Nxh7 26. Rxh7+ Qxh7 27. Qf6+ Rg7 28. Rxh7+ Kxh7 29. Qh4#. After the text move 23. ... a5, which is best, the last force, the white g-pawn, is thrown into the battle, and this leads to the combinative play I have analyzed above, and which is also contained in Walter Korn's book.
However, with the gain of the black queen the game is not over yet; Black can still put up a fight with his pawns. Theoretically, he has sufficient material for the queen; in this particular situation, however, his pieces are shattered and don't cooperate, so that White can conquer the bishop. For achieving this, however, it needs clever and study-like play. 30. Qg2! is the key move, after which Rb8 loses at once to Qh2+. But since Black's reply Ra7 loses the bishop quickly (as the text shows), wouldn't it have been better to play 30. ... Ra6 instead? Let us see: (30. ... Ra6) 31. Qh2+ Kg8 32. Qc7 Ra8 (if Be6, so 33. Qb8+ followed by 34. Qb7+) 33. Qc6 Rb8 34. Qxg6+ Kh8 (Kf8 35. Qd6+) 35. Qf6+ Kh7 (or Kg8 36. Qd8+ and 37. Qc7) 36. Qh4+ and 37. Qg3+, so that it this variation, Black is even worse off than in the actual game. So, it can be assumed, that Black deliberately preferred 30. ... Ra7 to gain time to play Rf7 and f4, and hence to rely on the f-pawn as his last chance (he can't save his c- and d-pawns, anyway).
White is then forced to blockade the black f-pawn with his queen. Then he chooses the simplest way to win: he returns the queen for the black f-pawn and the rook to achieve an elementary pawn ending. Can't Black stop that white plan by playing 38. ... g4 or 39. ... g4?
On 39. ... g4, 40. Qh4 wins, while on the immediate 38. ... g4 maybe 39. Ke1 threatening Qg3 is simplest, e.g. Kg6 40. Qh4 Rf4 41. Kf2.
In the game continuation, Black resigns since White will be able to establish two connected passed pawn which must be watched by the black king while they are able to protect themselves, so that the white king can leisurely conquer the black g-pawn and afterwards return to supporting his own men. A plausible continuation is 41. ... Kf5 42. c4 (of course, 42. a5, 43. c3, 44. b4 is possible, too) Ke5 43. b3 Kf5 (now it becomes clear that there is nothing in wandering to the queen side) 44. a3 Ke5 45. b4 axb5 46. axb4 Kd4 47. c5 Kd5 48. Kg4 etc.
So this masterpiece can be divided into 3 stages:
1) Preparation (till move 23)
2) Combination (moves 24-29)
3) Technique (moves 30-40)
It's a true model game in many respects, and as such it deserves to be much better known.