At the summit of Mount Tamalpais, Percy sees the resemblance between Atlas and Zoë as Zoë demands that Atlas release Artemis from the burden of holding the sky. Atlas explains that the sky must be held at this place where sky and earth first met, or it will crush everything nearby. Percy also notices that Annabeth’s hair has gray streaks from previously bearing the same weight.

Luke tries to persuade Thalia to join him by invoking their shared anger at the gods and promising that she can gain power by sacrificing the Ophiotaurus. Grover warns Percy through the empathy link to stop thinking about Bessie because Grover is struggling to keep the creature away. Luke reveals Kronos’s forces are gathering below and that they plan to rebuild Mount Othrys, attack Camp Half-Blood, and then Olympus, but Thalia rejects Luke and chooses to fight.

Percy, Thalia, and Zoë charge. Thalia battles Luke, while Percy attacks Atlas and is badly overmatched, especially when Ares’s old curse makes Riptide fail at a critical moment. Realizing he cannot defeat Atlas directly, Percy cuts Artemis’s chains and takes the sky from her, enduring unbearable pain so Artemis can fight the Titan.

Artemis duels Atlas while Zoë, already weakened by Ladon’s bite, aids with arrows. When Zoë intervenes to save Artemis, Atlas strikes Zoë aside, but Artemis uses Atlas’s own attack to throw him onto Percy. Percy releases the sky at the right moment, and Atlas is forced back under his ancient burden.

Meanwhile, Thalia defeats Luke and holds him at spearpoint. Annabeth begs Thalia not to kill Luke, hoping he can be taken to Olympus, but Luke taunts Thalia and grabs for the spear; Thalia kicks him away, and Luke falls from the cliff to the rocks below. Annabeth is devastated, and Kronos’s army begins attacking from below.

Artemis finds Zoë dying from the poisoned wound Ladon gave her, not from Atlas’s blow. Before the monsters can overwhelm the heroes, Annabeth’s father arrives in his Sopwith Camel and attacks the army with celestial bronze bullets. Artemis summons her silver chariot, and Percy, Thalia, Annabeth, Zoë, and Artemis escape into the sky with Dr. Chase escorting them, leaving Atlas trapped and raging beneath the sky.