King Hezekiah immediately gets to work building up defenses in all the most important cities in Judah. He's a good strategic thinker, but he also has one thing that the Assyrians don't—God is on his side.
He tells the people of Judah not to worry because God will help them out. Sure, he didn't help Israel or any of the other countless nations the Assyrians have smashed to bits, but he's totally going to help Judah.
King Sennacherib sends his people to Jerusalem to give the city a message—you're going down.
He throws some shade at Hezekiah, too. Their king is lying to them about God being able to protect them. Seriously, Hezekiah is so bad at ruling that he actually took down all the altars in Judah and just left this one in Jerusalem.
Look, King Sennacherib tells them, we've conquered a lot of nations. No god has ever been able to hold us back. What makes you think your God is different?
So King Hezekiah and the prophet Isaiah start to pray and God listens.
He sends an angel to kill a lot of people in the Assyrian camp. With his army depleted, King Sennacherib is forced to head back home. Later, his own sons kill him.
Hezekiah gets deathly sick and successfully prays to God for healing. He gets into some minor trouble with God, but repents and goes on to do all kinds of successful things as king.
God blesses him with immense wealth. Gold, gems, spices, weapons, food, wine, oil, and livestock—you name it, the guy has a whole warehouse full of it.
Finally, after a lifetime of righteousness, King Hezekiah dies. Everyone mourns him.