"The Hidden Oracle" is the first book in the Trials of Apollo series by Rick Riordan. The story follows Apollo, the once-powerful god, who is cast down to Earth in the form of a mortal teenager named Lester Papadopoulos. Stripped of his divine powers, Apollo must navigate the challenges of living as a human while searching for the Oracle of Delphi, which has gone missing. To regain his godly status, he teams up with a demigod named Meg McCaffrey, who has her own secrets and issues to confront.
The narrative combines adventure and humor, showcasing Apollo's struggles as he adapts to a mortal life filled with unexpected hardships. His interactions with various characters, including demigods and monsters, highlight themes of friendship, loyalty, and self-discovery. Through facing numerous obstacles, Apollo learns important lessons about humility and the value of human connection, paving the way for his growth as a former deity.