Zoë worries that the group is moving too slowly to reach the Garden of the Hesperides by sunset, the only time they can enter. Because Bessie the Ophiotaurus cannot come by car, Grover volunteers to guide him through the sea back toward Long Island, where Chiron can help protect him. Percy prays to Poseidon for safe passage and sacrifices the Nemean lion skin, recognizing that relying on Hercules’s trophy is not the kind of heroism he wants.

With Grover and Bessie gone, Thalia remembers that Annabeth’s father lives in San Francisco. Percy, Thalia, and Zoë visit Professor Chase, who turns out to be eccentric but caring, and Annabeth’s stepmother is kinder than Percy expected. After hearing that Annabeth is in danger on Mount Tamalpais, the Chases lend the group their car, and Mrs. Chase asks Percy to tell Annabeth that she still has a home with them.

Zoë drives the group toward Mount Tamalpais as sunset fades. On the way, Zoë explains that the mountain is connected to the defeated Titans and their imprisoned general. Percy sees Luke’s ship, the Princess Andromeda, docked below, confirming that Kronos’s forces are nearby. Moments later, Thalia senses danger and forces Percy out of the car just before a lightning blast destroys it, deepening Thalia’s fear that Zeus may be the parent foretold in the prophecy.

Zoë leads Percy and Thalia through the Mist into the Garden of the Hesperides. The garden holds Hera’s golden apples of immortality, guarded by the enormous dragon Ladon, and Zoë’s sisters reject her as no longer one of them. To create a path up the mountain, Zoë deliberately wakes Ladon and distracts him while Percy and Thalia skirt the garden. Ladon eventually attacks, and Zoë is wounded before Thalia’s shield gives her the chance to escape with the others.

At the summit, the group finds the ruined fortress of Mount Othrys, the ancient stronghold of the Titans, now reappearing on Atlas’s mountain. They discover Artemis chained and forced to hold up the sky, not a cave roof as Percy had seen in his dreams. Before they can free her, the General arrives with Luke, dracaenae carrying Kronos’s golden sarcophagus, and Annabeth as a bound hostage. The General reveals himself as Atlas, and Zoë confirms the deeper betrayal: Atlas is her father.