On the ferry with prisoners, one of the prisoners asked for the detonator from the policeman. All the people on that ferry thought that he was going to blow up the other ferry with innocent citizens but, upon getting the detonator, he threw it into the sea.
Meanwhile, on the ferry with innocent citizens, they conducted a poll and the majority chose to detonate the other ferry with prisoners on it. However, nobody came forward to detonate the bomb. Finally, a man stood up and said he would do it. Fortunately, he changed his bad idea at the last moment because nothing happened when the clock struck midnight. Both ferries were safe.
The Joker was battling with Batman and the former told the latter that they were going to watch a great firework display. The people on the ferries proved that the Joker was wrong.