The Trials of Apollo is a pentalogy of fantasy adventure and mythological fiction novels written by American author Rick Riordan that collectively form a sequel to the Heroes of Olympus series.

It is set in the same world as Riordan's Percy Jackson and Heroes of Olympus series and references characters and happenings from earlier stories.

Zeus is angry at Apollo for several reasons, most notably for giving his blessing to his Roman descendant Octavian, allowing the latter to rise to power during The Heroes of Olympus series.

[6] The book opens with Apollo landing in a dumpster in an alley in New York City, in the form of a mortal teenager named Lester Papadopoulos, because of the events leading up to the war between the Greeks and the Romans.

Believing that he must only undertake a simple quest to regain his immortality, Apollo and Meg travel to Camp Half-Blood with the help of Percy Jackson, where they learn that most of the world's oracles have stopped working.

The book continues the story of Apollo as the mortal Lester, as he leaves Camp Half-Blood and journeys across North America to restore the remaining four Oracles and learn how to defeat the Triumvirate of Roman emperors with the help of Leo Valdez, Calypso, Festus the bronze dragon, the Hunters of Artemis, and some new characters, including ex-Hunters Emmie and Jo and their daughter Georgina.

Apollo and Grover go to try to find Gleeson Hedge in an army store called Macro's Military Madness.

The book ends with Leo arriving from Camp Jupiter, learning about Jason's death, and Apollo and Meg going to San Francisco while Gleeson Hedge, his wife Mellie, their baby Chuck, Piper, and Piper's dad set off to Oklahoma, with a ride from Leo and Festus.

The story starts off with Apollo and Meg taking Jason's body to Camp Jupiter in the San Francisco Bay Area.

On their way, they are attacked by an eurynomos, but a girl with pink hair arrives with dryads and a faun and kills the eurynomous.

There is a funeral for Jason that night, and Lupa shows up to tell Apollo to get divine help to defeat their enemies.

They go to the camp senate, where he, Meg, Lavinia, and Hazel are selected to go on a mission to find out more about Tarquin, the final king of Rome, who has returned.

After they return, they realize that to solve the communication issues and get divine help, they need to destroy the soundless god.

Dakota, son of Bacchus and the longtime centurion of the Fifth Cohort, passes away overnight due to wounds from the battle.

While returning to New York, Apollo and Meg encounter an amphisbaena, which recites the second stanza of the terza rima prophecy.

Apollo and Meg reach Camp Half-Blood and the Grey Sisters recite another couplet of the terza rima prophecy.

After they discuss a way to sabotage Nero's Greek fire vats with the help of the troglodytes, a species of good diggers, Rachel suddenly spouts the final couplet of the prophecy, but Python has meddled with it.

Apollo, after managing to revive Lu, finds out that a leontocephaline, a creation of the Persian god Mithras, is guarding the fasces.

Upstairs, he realizes that the entire lower floor area has become a battleground, Camp Half-Blood demigods having come in.

Nero video calls the laptop and tells him that he has a plan B: to release Sassanid gas, which is extremely poisonous, and kill everyone in the building, unless Apollo comes to the throne room in fifteen minutes.

Meanwhile, Apollo reaches the throne room, where all the adopted children of Nero are present, including Meg.

Nero is given a choice, to fight a hopeless battle and die, or live for some more years in a large prison.

Camp Half-Blood's forces stay at the Tower to help rehabilitate the Imperial children after the years of abuse they endured, but Apollo has to go defeat Python.

Apollo is attacked by Python, but manages to throw him off the ledge into Chaos, destroying him forever and freeing the oracles from his power.

With the help of the troglodytes, Nico and Will intend to travel to Tartarus to find the source of the voice and rescue Bob if they can, and Rachel delivers a prophecy about this prospective quest.

Hazel gets rid of the curse on her summoned jewels so they can now be spent, and Percy and Annabeth are attending university there.

Reyna is there with the other Hunters of Artemis to hunt down the Teumessian Fox, as well as Leo, since Calypso is now in high school and had gone to a summer camp as a counselor.

Apollo also visits Meg, who is living in Palm Springs with Lu, the Imperial children whom she is teaching to garden, and the Meliae who are acting as security guards.

This book explores the story of one of the side characters, Claudia, a daughter of Cardea and descendent of Mercury, through her personal diary.

Rick Riordan has since collaborated with writer Mark Oshiro for a new novel in the Camp Half-Blood Chronicles, which follows Nico and Will travelling together to Tartarus to rescue Bob.