
Hazel is also upset with Jason and Leo because the two are hesitant in saving her half-brother, Nico di Angelo, who has been captured by the Giants during his travel to find the Doors of Death. Throughout the journey, tensions arise between the demigods, mostly between Leo and Frank, the latter of whom constantly becomes the target of jokes and teases by the former and is jealous of the former's friendship with his girlfriend, Hazel, when he learns that Hazel's previous boyfriend is Leo's identical great-grandfather. Percy, Frank, and Hedge also face Phorcys and his wife, Keto at the Georgia Aquarium while searching for information about Gaea's plans, with the latter sending one of her children, a giant Scolopendra, after them. With Gaea's directing, two Eidolons possess Percy and Jason, and later Leo, but both times they are repelled. Percy, Jason, and Piper meet with Bacchus at Kansas after hearing about his canceled appointment with Ceres. During the search, Leo meets with Nemesis, who presents him with a fortune cookie that would help him later, but with consequences. The seven demigods escape from Camp Jupiter and briefly land near the Great Salt Lake to search for celestial bronze, which they steal from a resurrected Narcissus. However, an Eidolon sent by Gaea possesses Leo and forces him to fire a blast on the camp, inciting the paranoid augur, Octavian, to convince the Romans that the Greeks are a threat and have to be destroyed. The statue can only be retrieved by the demigods of Athena through the help of the Mark of Athena, all of whom had died trying.

Annabeth, while having a talk with Camp Jupiter's praetor, Reyna, about the quest, reveals that in order to unite the Greek and Roman demigods against Gaea, they have to first retrieve the Athena Parthenos, a giant statue of Athena that was stolen by the Romans in ancient times and hidden somewhere in Rome. At Percy's request, Frank Zhang and Hazel Levesque are chosen as representatives of the Romans, alongside Jason, to accompany the Greek demigods. He, Jason Grace, Piper McLean, and Annabeth Chase, accompanied by Coach Hedge, arrive at Camp Jupiter to rendezvous with Percy Jackson and the Roman demigods.

Six months after the events of The Lost Hero, Leo Valdez has constructed a massive ship, Argo II for use in the seven demigods' journey to Greece to stop Gaea from awakening.
