Figure[White to move]

A horizontal study. White has the kernel of a discovered attack on the seventh rank; his rook is aimed toward Black’s king. Even if the path of the discovery is blocked for now by the bishop on g7, this configuration is a valuable asset and can guide the thought experiments that follow. Consider White's checks and their consequences. Qh6+ is most interesting, as the queen is protected; it forces either BxQ or Kg8. What next?

(a) If Black chooses BxQ, it clears the way for the discovered check we had hoped might materialize: now Ng5++ forces the king to h8 (notice that White’s bishop on b3 also participates). And then Rh7 is mate.

(b) If Black plays 1. …Kg8 instead of 1. …BxQ, then 2. Qh8+, BxQ; 3. Nh6# likewise is mate via discovery—this time using the bishop on b3, which the knight also was masking. The queen sacrifice on h8 serves to leave that square blocked, further constraining Black's king.

The trick to the position is seeing that the knight masks pieces in two directions, both aimed in the enemy king's vicinity. This creates multiple chances for game-ending discovered checks once Black's king is pushed around a bit. More generally it's a valuable study in the importance of thinking beyond the two obvious pieces in a discovery; White finally uses four pieces to wrap this position up.