White to move. The features that stand out are the absolute pin on black's pawn at g6, the potential pin against the black queen on the same diagonal as its king, black's vulnerable 7th rank, and the fact that the pinned pawn is attacked and defended 3 times so that removing a guard from g6 will lead to the win of material (the same point is true of the pawn on f5, which turns out to be the key to the solution).White plays: 1.Rxd4!
"The forcing, violent move - a capture - initiates action on the long diagonal." -- Reinfeld
1...exd4
This move is forced. Otherwise Black will remain a rook behind. The next move is the tougher one to see.
2.Bxd4!
The Pin. The queen screens the king from attack but cannot move away.
2...Qxd4
The capture of the white bishop is forced, setting the stage for the decisive knight-forking check.
3.Nxf5+
"This forcing violent knight-forking check wins black's queen because the king knight pawn is pinned..." -- Reinfeld
SOURCE -- The Secret of Tactical Chess:
A Manual of Chess Victory by Fred Reinfeld (1958), Collier Books (1973), softcover, diagram 85, page 129.The themes are pin and knight fork (double attack). This was one of the first books on chess tactics that I studied. It was republished by Collier during the Fischer-Spassky boom in Great Britain and the United States. Note the cover price of $2.45. The same book would be released at ten times that much today.
