Another variation on the same idea, this time from Black’s side. Where does Black have the makings of a discovered attack? On the long a8-h1 diagonal. As usual the rook masks the queen, and if it were moved Black could play QxQ. The important question involves what to do with the rook. Again it has no checks, so consider the White king and its vulnerabilities. Here as in the previous position it is stuck on the back rank, as Black’s bishop on h3 cuts off its escape. And once more the king has a single guard: the rook on e1. If Black threatens that rook with his own, he threatens mate. So he has two possibilities, either of which works: 1. …Rd1 or 1. …Re5.

There is a little more to say, because you always must ask whether your opponent has a way to both move the targeted piece out of danger and spoil the mating threat. White's queen can't move to the east because Black then threatens to mate with Qg2. But in response to either of those rook moves we have sketched, White can play 2. Qxh3, avoiding QxQ and preparing to interpose the queen on f1 if Black plays RxR. But then he still loses the queen—and also both rooks. It goes 2. …RxR+, 3. Qf1, RxQ+, 4. KxR, QxRh1+. Black has a queen left and White has nothing.