Hezekiah, on hearing the news of the Assyrians' threats, tears his clothes. Then he sends a delegation, in sackcloth, to the prophet Isaiah, to ask him to pray to god. Isaiah tells them not to be afraid, because the Assyrians blasphemed god and god is going to take his revenge by killing the general after he goes home.
So they return and find the Assyrians fighting in Libnah. The Ethiopian (or possibly Egyptian) king arrives to help the Israelites. The Assyrian king sends a taunting message to Hezekiah telling him not to expect Jerusalem back, because he's destroyed plenty of other countries whose gods didn't help them.
Hezekiah goes to the temple and prays. God sends word back via Isaiah that he got the message, and he's happy to help. He insults the Assyrian king for awhile then threatens him. He also promises to restore Judah in 3 years' time.
Then the angel of the lord goes and kills 185 000 Assyrians in their sleep, like, they didn't have watchmen? The general escapes to Assyria, only to be killed by his sons while praying. The sons then go to Armenia.