Black queen takes the knight on C3, putting white in check while threatening the rook. With the bishop on A4 and the knight on D4, the white king can only move to F1/2. Blocking with the bishop is ineffective since then the queen will just take the rook to maintain check.
When the king is moved (regardless if F1 or 2), the black knight moves to H7, opening the column for check through the rook, while threatening the queen. Queen can't block on F4 (unprotected), so the white king has to make a run for it or use the knight to block, white queen is gone, white rook and bishop still threatened through the black queen.