BoHaShem tells Moshe that He is hardening Pharaoh's heart so that through miraculous plagues the world will know for all time that He is the one true G-d. Pharaoh is warned about the plague of locusts and is told how severe it will be. Pharaoh agrees to release only the men, but Moshe insists that everyone must go.
During the plague, Pharaoh calls for Moshe and Aharon to remove the locusts, and he admits that he has sinned. HaShem ends the plague but hardens Pharaoh's heart and again Pharaoh fails to free the Beney Yisrael. The country, except for the Jewish People, is then engulfed in a palpable darkness.