Figure[White to move]

Notice the diagonal alignment of Black's bishop and rook, and that White can run his own bishop through both of them with Bb4. A bishop skewering a bishop is no good, but it invites a look for productive substitutions. Here NxB+ provokes the recapture QxN, luring the queen onto the same dark-squared diagonal with its rook. White swoops in with his dark-squared bishop on b4, where it makes a protected skewer of Black’s queen and rook and, again, wins the exchange next move.