The Jews wanted Paul back to Jerusalem for another ambush, but he didn't go. When Festus couldn't figure out the charges against Paul, he suggested Paul go back to Jerusalem. That's when Paul appealed to Caesar.
While he was held, Agrippa came to town. One thing led to another and the king asked to hear from a prisoner. How weird is that? I guess if you don't have TV you have to find something to do for entertainment. All this took place in the context of great pomp and circumstance.