Do you see the skewer for White? Which one? When a king ventures out into the middle of the board late in the game, it can become prey to multiple skewers as its fellow pieces often end up behind it. Here you can see that Black’s king is in front of its bishop, rook, and queen. White can skewer any of them. The queen can check the king along two diagonals, its rank, and its file. Thus Qc2+ wins Black’s bishop; Qe2+ wins a rook; Qg2+, best of all, wins the queen. (Notice that since White is down a rook and a pawn, only the availability of Qg2+ saves the game.)