Against the backdrop of this awful judgment is a verse that reveals God's protection of His own: "Only in the land of Goshen, where the children of Israel were, was there no hail" (Ex. 9:26).
Goshen was part of Egypt, but God controlled the circumstances so that the Israelites were untouched by the judgment that Egypt experienced.
Notice what Pharaoh's response was to this awful judgment: Although Pharaoh seemed to be conscious of his wickedness before God, it was only a feigned confession made in order to escape judgment.
Moses was not fooled by Pharaoh's false confession. God had given Moses insight so he knew what was in Pharaoh's heart and was not fooled in any way.
This reveals how hardened Pharaoh really was; it did not bother him even to fake a confession of sin to God. But God knows what is in each person's heart, and He was not deceived for one minute.
God had showered His mercies on Pharaoh, but Pharaoh had refused to respond positively in any way. So in the remaining plagues God further hardened Pharaoh's heart so as to fulfill His plan of total revelation of Himself as absolutely sovereign.
"Shall not God search this out? for he knoweth the secrets of the heart" (Ps. 44:21).