Exodus 11:10

And Moses and Aaron did all these wonders before Pharaoh, c,] Which are related in the preceding Chapter s:

and the Lord hardened Pharaoh's heart: one time after another, and yet more and more:

so that he would not let the children of Israel go out of his land until the last plague, the slaying of the firstborn, was brought upon him and his people, related in the following chapter.