A difficult two-mover

This is from my book "White to Play" by Alain White. First, note the set play. If BQ plays along diagonal, you have Qxh7 mate, and if QxQ Sf2 mate. Other black pawns are pinned or blocked, and if the bishop moves you have Qb1 mating.

So that is a block. Can you preserve the waiting nature of the problem with any quiet move? Try as you might, you cannot.

So please move the mouse over, or click on the 1.? to see the solution. After the key, white threatens Rg4 mating. We now have the changed mates or added mates, exd4 Qd5 mate, Kxd4 Qb4 is cute, original mates Qb1, and Qxh7 are still in play after the other two captures on d4 to prevent the threat.

The above kind of problem is called a block-threat. Very deceptive and very hard to solve, but with a sharp intake of breath or "aha" feeling when you solve it.