The Trials of Apollo 5: The Tower of Nero

"The battle for Camp Jupiter is over. New Rome is safe. Tarquin and his army of the undead have been defeated. Somehow Apollo has made it out alive, with a little bit of help from the Hunters of Artemis.

But though the battle may have been won, the war is far from over.

Now Apollo and Meg must get ready for the final and, let's face it, probably fatal adventure. They must face the last emperor, the terrifying Nero, and destroy him once and for all."