Published in 2012, The Mark of Athena is the third novel in Rick Riordan’s young adult fantasy series The Heroes of Olympus, his second series in the Percy Jackson universe inspired by Greek and Roman mythologies. The Mark of Athena picks up the narrative where The Son of Neptune left off, with a Greek warship from Camp Half-Blood approaching Roman Camp Jupiter in hopes of collaborating to stop Gaea from waking up and destroying the gods. The novel follows seven demigods from both camps as they undertake a quest to Rome to find Nico and the Mark of Athena. It is narrated in third person limited omniscient from the points of view of four Greek demigods: Annabeth, Leo, Piper, and Percy. Joining them on the quest are Roman demigods Hazel, Frank, and Jason.

This study guide refers to the 2012 edition published by Hyperion Books.

Plot Summary

Annabeth and her counterparts from Camp Jupiter convince Hazel, Frank, and Percy to join them on the quest to Rome and Greece on the warship Argo II, but spirits possess Leo’s body and use him to fire on the city. The group flee New Rome.

To repair damage the ship sustained, the demigods stop at a lake that promises to have the celestial bronze Leo needs. In their search, he and Hazel meet the goddess, Nemesis. If the demigods accept her help, they may be able to avenge an old wrong. Hazel and Leo receive help from Echo to wrest a sheet of celestial bronze from Narcissus, who is using it as a mirror.

The ship heads to Kansas, where Bacchus turns down their request for help but suggests they visit the old sea god Phorcys in Atlanta. After Bacchus leaves, eidolons at Gaea’s command possess Jason and Percy, and they almost kill each other. Back on the ship, Piper realizes the eidolons are still present and extracts an oath from them promising never again to possess the demigods.

As the ship heads for Atlanta, Percy has a dream in which Nico is trapped in a bronze jar. When he relays the dream to the others, they understand that this image is connected to the prophecy, and the must find Nico before his time runs out. In Atlanta, Percy and Frank learn that Phorcys is working with Gaea and almost become trapped in his aquarium. They manage to escape with a clue that leads to Charleston.

During Annabeth’s last meeting with her mother, Athena, the goddess had seemed confused and angry and insisted that Annabeth avenge Athena against the Romans. Annabeth joins Piper and Hazel on a trip to the Battery in Charleston, where they meet with Piper’s mother, Aphrodite/Venus. Annabeth realizes that Athena wants her to recover the Athena Parthenos, a famous ancient statue of Athena that the Romans stole when they conquered Athens. Their Roman pursuers find them, but Annabeth manages to recover the map. The demigods reconvene on the ship and head to the open sea.

Leo and Hazel figure out that his great-grandfather was a childhood friend of Hazel’s who believed he had inadvertently caused her death. They return to the ship just as it is being attacked by a sea monster. Leo and Hazel defeat the monsters using Greek fire but are knocked out in the attack. When they awake, they are being held prisoner under the sea by fish centaurs, but the creatures are not hostile. When they confirm who Leo and Hazel are, they let them go with a letter of introduction for Annabeth to the Roman river god Tiberius.

The following morning, the demigods wake up at the Pillars of Hercules, the entrance to the Mediterranean Sea that is guarded by Hercules himself. Piper and Jason meet with him. Initially, Hercules is helpful, but when he learns their quest is at Hera’s behest, he becomes hostile. The demigods work together to get past Hercules and enters the Mediterranean.

In the Mediterranean, the demigods are pursued continuously by various monsters. In Rome, Percy accompanies Annabeth to the river where she meets with Tiberinus, who brings her to the Emmanuel building where her quest will begin. Descending deeper and deeper underground, Annabeth breaks her ankle, fights through a group of ghosts in Gaea’s service, and finally comes face-to-face with Arachne, her mother’s archenemy who guards the Athena Parthenos.

The other demigods continue their search for Nico. Frank, Hazel, and Leo explore the Pantheon. Elsewhere in Rome, Piper and Jason are celebrating his birthday when Percy finds them, worried about Annabeth. Looking into Katoptris, Piper sees an image of Nico at the Forum, now out of the pomegranate seeds he needs to stay alive. The trio decide his needs are the most urgent and head for the Forum.

Percy, Jason, and Piper come face-to-face with giant twins Ephialtes and Otis, who work for Gaea. The twins have planned a gory, gladiatorial-style death for the demigods, but Jason and Percy hold them off. Bacchus shows up to finish off the giants. They rush back to the Argo with Nico and set their course for the Emmanuel Building, having been prompted to do so by Bacchus.

Annabeth stalls for time and eventually tricks Arachne. Furious, Arachne’s throws herself around the chamber, which sits above Tartarus. She tumbles into the abyss but remains connected to Annabeth by some threads that become entangled around Annabeth’s feet. The Argo arrives, and Percy grabs her. The two fall together, leaving their friends stunned and grieving.