Figure[Black to move]

The classic execution of the current idea starts with a queen and bishop both aimed at the pawn on f7 or (against White) f2—the edge of the castled king’s pawn cover. Black has the formation here just as White did in the previous position; the difference is just that Black's queen comes in from the side instead of attacking down the f-file. The result is the same: Black starts with Qxf2+, forcing the reply RxQ to prevent immediate mate—but now White’s rook is pinned and his back rank is open for Black's Rd1#.