King Josiah arranges for everyone to come to Jerusalem for Passover, just like Hezekiah did. The celebration's a big success and everything's carried out according to the laws of Moses from the recently discovered book.
Everything would have been perfect if the King of Egypt hadn't been out and looking for a fight.
King Josiah heads out to do battle with him. But the King of Egypt isn't interested in conquering Judah. He tells Josiah to head back home because he's about to attack another nation.
The King of Egypt even emphasizes that God himself told him to hurry up and attack these other people. If Josiah keeps coming at Egypt, then he's opposing God.
Poor Josiah doesn't listen and he heads into battle anyway. Josiah is shot by arrows and brought back to Jerusalem, where he dies.
Despite this, Josiah has a reputation as a reformer. Everyone in Judah is just broken-hearted when he's killed. People sing all kinds of sad songs for him, and the great prophet Jeremiah himself composes a special lament for Josiah, which, the Chronicler tells us, is sung even "to this day."