The following version of this book was used to create this study guide: Riordan, Rick. The Trials of Apollo, Book One: The Hidden Oracle. Disney/Hyperion. 2016. First Edition, May 2016.

The Trials of Apollo, Book One: The Hidden Oracle is a young adult fantasy novel by Rick Riordan. It is the first in Riordan's Trials of Apollo series. Rooted in mythology, the novel begins as Apollo is blamed for the civil war between Greek and Roman gods after one of Apollo’s sons was tricked into beginning the war. As punishment, Apollo is made mortal and plummeted to Earth. He lands in Manhattan as a mortal where he is no longer an invincible, handsome, muscular god. Instead, Apollo is a geeky, curly-haired, flabby sixteen year-old whose name is Lester Papadopoulos. Apollo is attacked by two punks who say they were sent by their boss. A twelve year-old girl named Meg pelts the punks with fruit and saves Apollo.

Apollo quickly learns Meg is a demigod. Meg claims Apollo as her servant. Apollo explains his predicament. He wishes to get to Camp Half-Blood, out on Long Island, hoping old friends can help him in his situation. To get there, they will need the help of Percy Jackson, demigod son of Poseidon. Percy drives them most of the way, but dark forces attempt to derail them. Meg saves the day by summoning a creature made from peaches. The creature destroys the forces after them. At Camp Half-Blood, Apollo learns from two of his teenage children (Austin and Kayla) and the temporary director (Chiron) that a number of student campers have gone missing.

Through all of these events, Apollo experiences things he has never experienced before because he is now mortal. For example, he is amazed when he bleeds. He is also stunned to have feelings of sadness and guilt. The lives of his children now mean more to him as mortality makes him aware of the others around him. It makes him a more caring, mature person.

Also, while at Camp Half-Blood, Apollo participates in a race to find golden apples with the other campers by using a racecourse that opens up into the Labyrinth. There, Apollo and Meg discover the plans of the Beast, formerly known as Roman Emperor Nero, who seeks to control all the Oracles in the world to prevent the Greek gods and demigods from hearing and interpreting prophecy. Without hearing prophecies, they will have no future. Nero kidnaps Austin and Kayla to antagonize Apollo. Apollo is one of the few who can open the gates to the oldest Oracle of all, the Grove of Dodona. Eventually, Meg herself is kidnapped.

Apollo sets off after Meg and learns that Meg is the half-daughter of Nero himself. Meg has betrayed Apollo by enticing him to come after her. Meg is not happy about this, but she loves her father. Nero attempts to burn the Grove using the disappeared campers as human torches, but Apollo manages to stop him, saving the Grove and the campers. They then rush back to Camp Half-Blood, where a giant bronze statue of Nero dressed as Apollo seeks to destroy the camp. Using a flying chariot and a plague-enchanted arrow, Apollo shoots the statue in the ear, giving it a cold and causing it to sneeze its head off and die. That night, as the campers celebrate, Apollo knows he must set off after Nero and his cohorts to find Meg.