The Trials of Apollo Tome 2
The Dark Prophecy

Zeus has punished his son Apollo by casting him down to Earth in the form of a gawky sixteen-year-old mortal named Lester. The only way Apollo can reclaim his rightful place on Mount Olympus is by restoring several Oracles that have gone dark. But how can Apollo/Lester do anything about them without his powers ? After experiencing a series of humiliating trials at Camp Half-Blood, Lester must now leave the safety of the demigod training ground and find the most dangerous Oracle from ancient times : a haunted cave that may hold answers for Apollo in his quest to become a god again—if it doesn't kill him or drive him insane first.
Standing in Apollo's way is the second member of the evil Triumvirate, a Roman emperor who makes even Nero look tame. To survive the encounter, Apollo will need the help of son of Hephaestus Leo Valdez, the now-mortal sorceress Calypso, the bronze dragon Festus, and other unexpected allies—some familiar, some new—from the world of demigods. Come along for what promises to be a harrowing, hilarious, and haiku-filled ride....