Festus was a very different man than Felix: he was just and upright. We can see here that the Jews, immediately he took office, tried to take advantage of him, but Festus insisted that Paul stay put and the Jews go to Caesarea. The implication from Paul's reply here is that the Jews had accused Paul of heresy, sacrilege and treason: the first accusation from their point of view may have had some truth, but the other two were downright lies. Obviously, Festus had to keep the Jews on his side in the early days of his office, so he offered Paul the opportunity to go to Jerusalem. Paul knew that he would never receive a just outcome there, so he appealed to Caesar. A Roman citizen, if they felt they were not receiving justice in a provincial court, could do this and so Paul was headed for Rome.
Agrippa was King of quite a small area of Palestine and was dependent on the Romans even for that small realm. He therefore came to visit the new governor and Festus asked him about Paul's case. Agrippa's wife, Bernice, was sister to the wife of Festus and so there was already a blood connection. Festus had rather a quandary as any Roman citizen who appealed to Caesar had to be sent to Rome with a written account from the governor of the area he was arrested in of the charges against him. In Paul's case, Festus could not identify that there were any charges!
This appearance, described in verses 22-27 would have been one of splendour. Agrippa and Bernice would have dressed with the purple robes of royalty and Felix would have donned scarlet too. The place would have been full of military commanders, influential Jewish figures and the retinue of the royal figures. Paul would have stood, his hands in chains, a little man by all accounts and yet he holds the stage, a charismatic figure undaunted by the splendour around him and sure of one thing: he is prepared to live and die for his Lord.