Percy returns from the Underworld to New York with Mrs. O’Leary and calls Annabeth, who is leading Camp Half-Blood forces toward Manhattan as Percy requested. At the Empire State Building, about forty campers arrive with Chiron, Argus, and the camp vans, but the Ares cabin is absent. Chiron refuses to enter Olympus unless summoned and tells Percy that Percy, not Chiron, is now the campers’ leader.

Percy leads the campers to the six-hundredth floor and into a strangely silent Olympus. The empty streets and nervous minor immortals suggest that the gods’ absence has left the mountain vulnerable. In the throne room, Hestia greets Percy, recognizes that Percy now carries the curse of Achilles, and warns that Percy is still blind to an important truth.

Hestia gives Percy a vision of Luke and Thalia finding seven-year-old Annabeth after Annabeth has run away from home. Luke gives Annabeth the Celestial bronze knife she still carries and promises that Annabeth is part of his family. The vision shifts to Luke bringing Thalia and Annabeth near May Castellan’s house in desperation, where a golden light and a man’s voice warn Luke that Luke should not have come home.

Hermes appears after Hestia leaves, and Percy sends the other campers away so that Percy and Annabeth can speak with Hermes privately. Hermes explains that Athena suspects Kronos’s attack on Manhattan is a trap, but Zeus will not recall the gods from the battle against Typhon. Hermes relays Athena’s messages: Annabeth must use “plan twenty-three,” Percy must “remember the rivers,” and Percy should stay away from Athena’s daughter.

When Annabeth apologizes for Luke, Hermes erupts in anger and blames Annabeth for not saving Luke when Annabeth had the chance. Percy defends Annabeth by accusing Hermes of abandoning Luke and May, nearly provoking Hermes into striking Percy until George and Martha, the snakes on Hermes’s staff, calm Hermes down. Hermes leaves in grief, and Annabeth breaks down; Percy then tells Annabeth about visiting May Castellan, while Annabeth realizes that Percy has bathed in the River Styx and connects Luke’s survival to the same power.

Annabeth opens Daedalus’s laptop and finds Athena’s plan twenty-three, which involves dangerous inventions and confirms the severity of the crisis. The Stoll brothers interrupt and bring Percy and Annabeth outside, where the campers discover that Manhattan has gone completely silent. Looking through the binoculars, Percy sees pedestrians and drivers asleep across the city and realizes that Morpheus has fulfilled the prophecy’s warning of “endless sleep”: Kronos’s invasion has begun.