The key character of this story is Moses. After Pharoh gave the order to kill all young male Jews in Egypt, his mother put him in a sealed basket, and sent him down the river. The Pharohs daughter found the basket with Moses inside, and took him as her own.
When Moses was grown, he was contacted by God, who appeard in the form of a burning bush, and commanded him and his brother to "ask" Pharoh to "let his people go!"
After of few magic tricks, and a slaughter, Pharoh agrees to let the Jews go, and they begin their 40 year desert wander.
"And the LORD said unto Moses, When thou goest to return into Egypt, see that thou do all those wonders before Pharaoh, which I have put in thine hand: but I will harden his heart, that he shall not let the people go." (4:21, KJV)
As you can see by the above, God intentionally makes the Pharoh stubborn, seemingly so that he has an excuse to effectively destroy a population. This apparent evilness flatly contradicts the Christian idea of an omnibenevolent god.
God calls down a series of plagues, strifes, and evils on the population (who, incidentally, had nothing much to do with the Jews enslavement).
Rivers of Blood
The first plague that Jaweh calls on the people of Egypt is to turn all of the waters into blood. The fish die, and the people of Egypt cannot drink.
God fills the land of Egypt with frogs. The frogs fill the ovens, and kneeding pots, and bedrooms, and clamber onto