Exodus 11:1

And the Lord spake unto Mosheh, Yet one stroke will I bring upon Pharoh and upon the Mizraee, which shall be greater than all, and afterward will he send you hence: when he releases, there shall be to himself an end: driving, he will drive you forth from hence.

AND THE ETERNAL SAID UNTO MOSES: YET ONE PLAGUE MORE WILL I BRING UPON PHARAOH. “This [prophecy] was spoken to him while he was still standing before Pharaoh, for after he left him he did not see his face again.” Thus the language of Rashi.
Our Rabbis have similarly said: “G-d sprung upon Moses. He, as it were, entered Pharaoh’s palace, [which was replete with abominations], for the sake of Moses — who had said, I will see thy face again no more — so that Moses might not be branded a liar. Now you find no other occasion on which the Holy One, blessed be He, spoke to Moses in the royal palace except this moment. Whence may we deduce this? From the verse, As soon as I am gone out of the city, I will spread forth my hands unto the Eternal., 9:29. And see Ramban there. But now the Holy One, blessed be He, sprang upon Moses and said to him, Yet one plague more, etc.”
Now here too there is a shortening of narrative. G-d said to Moses, Yet one plague more will I bring upon Pharaoh, and He informed him of the nature of that plague, saying to him, At midnight I will go out into the midst of Egypt, as well as the whole communication stated in this section, [further in Verses 5-8, as Moses’ address to Pharaoh in the Name of G-d]. But Scripture did not want to lengthen the account by first narrating what G-d said to Moses, it being sufficient to state what Moses said to Pharaoh, i.e., Thus saith the Eternal, just as I have explained in the case of the locusts. There are many such sections in the Torah. In this Seder (section of the Torah), in the segment, Sanctify unto Me all the firstborn, Scripture shortens the subject which the Holy One, blessed be He, communicated to Moses, and it prolongs the account of Moses’ words to the people, i.e., Remember this day, etc.,, Verse 3. and so on to the end of that entire segment. They really are G-d’s words to Moses, which he said to Israel in the very language with which he was commanded.

(1) ADONAI SAID TO MOSHE while he was standing in front of Par'oh, "ONE MORE PLAGUE, ETC." And after that, Moshe responded to Par'oh (v.4), "Thus says the LORD: At midnight, etc."

(2) ONE AND ALL (KALAH). All -- men, women, children, and livestock.

ישלח אתכם מזה כשלחו, in the same manner as he has already expelled both you and Aaron from his presence when he had lost his cool. (compare 10,11). When he will send the whole people of Israel from his land, he will act under a similar type of stress.

כלה גרש יגרש אתכם, at that time he had only expelled the two of you. This time he will expel all of you from this entire country. This is the attribute of G’d’s justice at work. When a person obstinately insists on not performing the expressed will of his Creator, (owner) he will ultimately have to do what he tried to avoid doing under infinitely worse circumstances. The Torah had warned us in Deuteronomy in Moses’ famous speech of admonition that because the Jewish people had refused to observe G’d’s commandments joyfully, out of a feeling of gratitude for their success in the Holy Land, they would ultimately still have to do what G’d wanted them to do, and what they had contracted to do, by serving G’d’s servants [host nations in the land of our exile. Ed.] instead of Him directly. (Deut. 28,47-48). Our sages phrase it thus: “everyone who ignores and fails to observe Torah pleading his wealth as his excuse, will ultimately keep the Torah because he has become impoverished.” (Avot 4,10) He will then be so preoccupied with keeping body and soul together that he has no time to devote to Torah study and observance. Numbers 14,28 also outlines the principle of retribution matching the nature of the sin.

ויאמר ה'....עוד נגע אחד, “the Lord said:....”one more plague;” what is meant is that G–d told Moses that after Moses would leave Pharaoh now, he would not see him again. In light of what is written later, we must assume that G–d lifted Moses at least ten handbreadths above the soil of Egypt on account of the state of ritual pollution that existed in Egypt.