Formerly the Olympian god of the sun, music, archery, and prophecy, Apollo has been cast down to Earth as a punishment by his father, Zeus. Now inhabiting the body of a 16-year-old mortal named Lester Papadopoulos, he struggles with his new lack of powers, mortal flaws like acne, and confusing human emotions. He must navigate the modern world without his divine abilities while searching for a way to restore the silenced Oracles.

Meg is a 12-year-old demigod who wears mismatched clothing, including cat-eye glasses and crescent rings. She is stubborn, secretive about her past, and fiercely commands Apollo after claiming his service during the alley fight. She demonstrates unusual abilities with agriculture and food, suggesting a powerful mythological lineage.

Nero is a notoriously cruel historical Roman emperor who has secretly survived into modern times by tying himself to Western civilization. He is the wealthy, ambitious leader behind Triumvirate Holdings, a massive corporation aiming to monopolize the silenced Oracles. He uses vast resources and ancient mercenaries to achieve his goals of absolute domination.

Percy is a powerful demigod son of Poseidon. Trying to balance studying for college entrance exams with his chaotic demigod life, he reluctantly helps escort Apollo and Meg to Camp Half-Blood. He is practical, experienced, and weary of getting pulled into further world-ending quests.

Peaches is a karpos, or ancient grain spirit, who appears as a feral, baby-like creature wearing a linen diaper. Though he looks somewhat cuddly, he possesses vicious teeth and acts aggressively toward anyone who threatens Meg. He represents the raw, untamed power of nature.

Rhea is a Titan queen and an older-generation goddess of fertility. She appears in the modern world as a quirky, Bohemian woman running a pottery studio in Upstate New York. She offers critical guidance to Apollo regarding the Oracles and the true nature of his enemies.

Leo is a demigod son of Hephaestus who vanished months prior to Apollo's arrival, following a major battle with Gaia. His absence leaves the campers angry and worried, as he is known to be an essential ally. He is the subject of intense search efforts by his younger brother.

Will is a demigod son of Apollo and the head healer at Camp Half-Blood. He is responsible, caring, and currently older than the teenaged mortal form his father occupies. He works tirelessly to heal the campers during a string of dangerous crises.

Nico is a demigod son of Hades who carries a distinct aura of death around him. He is highly perceptive, instantly recognizing Apollo's new mortal vulnerability and the dangers surrounding the camp.

Percy's mother is seven months pregnant and exceptionally hospitable. She provides Apollo and Meg with a warm welcome, clean clothes, and her famous seven-layer dip, treating the fallen god with the same kindness she shows human guests.

Harley is the eight-year-old demigod son of Hephaestus. Despite his young age, he is mechanically gifted and designs dangerous obstacle courses for the campers while working on a tracking device to find his lost brother.

Calypso is an ancient nymph who was previously trapped on the island of Ogygia. Having relinquished her immortality to leave the island, she currently navigates life alongside Leo Valdez, embracing the freedoms and risks of a mortal existence.

Rachel is a mortal teenager who serves as the Pythia, the priestess of the Oracle of Delphi. She is deeply troubled by her recent inability to issue prophecies and seeks answers regarding the mysterious corporation threatening the demigods.

Pete is a palikos, or geyser god, made of mud and steam. He acts as an overly enthusiastic marketing representative for the camp's woods and avoids direct combat with the dangerous creatures lurking nearby.

The king of the gods, known for his temper and harsh disciplinary methods. He casts Apollo down to Earth in a mortal body as retribution for the recent war between Roman and Greek demigods.

Chiron is an ancient centaur and the long-time activities director at Camp Half-Blood. He struggles to keep the camp functioning amidst failing communications, the silenced Oracle, and a sudden string of demigod disappearances.

Kayla is a demigod daughter of Apollo who inherited her father's talent for archery. She serves as an instructor at the camp and tries to encourage Apollo when he becomes frustrated by his sudden mortal limitations.

Austin is a demigod son of Apollo with a natural gift for music. He is supportive of his father's new mortal form and actively assists the camp during crises.

Cade is a young thug with a serpent tattoo on his arm. He attempts to mug the newly mortal Apollo before being chased off by a barrage of rotting fruit.

Mikey is a street thug bearing a snake tattoo who assists Cade in beating up Apollo. He is quickly frightened away when Meg intervenes.

Vince is a seven-foot-tall Germani, an elite imperial bodyguard from ancient Rome. He bears a serpent tattoo and relies on brute strength to enforce Triumvirate Holdings' orders.

Gary is an ancient Roman Germani bodyguard working for Triumvirate Holdings. He relies on his massive size and combat skills to protect his leader.

Mama is the massive queen ant of the myrmekes. Despite her terrifying, barbed appearance, she displays a maternal instinct and responds surprisingly well to musical appeasement.

Connor is a demigod camper who attempts a prank on Meg shortly after her arrival. His actions inadvertently trigger a violent response from her hidden protector.

Sherman is a burly demigod son of Ares who runs the morning boot camp. He is highly disciplined but falls victim to the strange, trance-inducing voices calling from the woods.

Python is an ancient, giant snake-like monster who has recently seized the cave of Delphi. He effectively cuts off the primary source of prophecy for the demigods, acting as a major roadblock in Apollo's path to redemption.