2 Kings 18-19: King Hezekiah cleans house, but caves to the Assyrians. He then calls out to God.

King Hezekiah finally takes down the high places and rids Israel of idolatry. He is only one of three kings favorably compared to King David.
The kingdom grows and prospers under his leadership, but he panics when the Assyrians start to invade and capture some towns. He offers tribute to stop the advance, but then Sennacherib wants to accomplish in the south (Judah) what his father accomplished in the north (the complete destruction of Israel).
Sennacherib besieges Jerusalem, and Hezekiah realizes he has been had. There is no recourse, and he turns to Isaiah in complete despair.
Isaiah responds that the threat is just words, and that the armies will soon retreat -- which they do. Then word is sent to Hezekiah to tell him the threat is not over, and that Judah is about to be destroyed.
This time Hezekiah turns directly to the Lord, and after his prayer, Isaiah shows up to tell him that God will save -- after which 185,000 Assyrians are killed in one night by an angel.
The rest of Isaiah's prophesy comes to pass when Sennacherib is killed by his own men at home in his own, pagan, temple.