After Morpheus puts Manhattan to sleep, Percy, Annabeth, and the campers regroup with Argus and Mrs. O’Leary. Argus gives Annabeth a bronze viewing shield based on Daedalus’s work, allowing the campers to survey the city by reflected natural light. Percy sends Argus back to guard Camp Half-Blood and sends Mrs. O’Leary to find Grover, knowing the defenders will need every ally available.

Using the shield, Annabeth discovers that Kronos’s forces are attacking Manhattan from multiple directions: demigods in boats near La Guardia, monsters and telkhines coming by ferry through the harbor, and a large force with a Sherman tank entering the Lincoln Tunnel. Annabeth also realizes Manhattan is asleep while the surrounding area is slowed by time magic, leaving the island cut off from outside help. Percy accepts that their small force must hold Manhattan alone.

Percy organizes the cabins to defend the major bridges and tunnels, assigning Apollo, Demeter, Hermes, Aphrodite, and Hephaestus campers to key entry points. The absence of Clarisse and the Ares cabin creates a gap at the Lincoln Tunnel, but Thalia arrives with the Hunters of Artemis, wolves, and falcons. Thalia takes responsibility for the Lincoln Tunnel, giving the demigods a crucial reinforcement.

Before leaving, Percy rallies the campers for Olympus, then travels with Annabeth through the eerie sleeping city on a borrowed Vespa. Along the way, they move sleeping mortals out of danger and respond to small hazards. In Madison Square Park, Annabeth activates one of Daedalus’s hidden automaton statues, beginning plan twenty-three so the city’s statues will awaken and, hopefully, defend Manhattan.

At Battery Park, Percy enters the harbor alone to negotiate with the East River and Hudson River gods. After provoking them into appearing and surviving their attack because of the curse of Achilles, Percy offers them Poseidon’s sand dollar. He breaks it in half so each river god receives part of its cleansing power, and in exchange they agree to sink Kronos’s boats and keep enemy forces off the rivers.

Percy returns to Annabeth and reports that the rivers are secure, but Annabeth has just received worse news from Michael Yew. Another army is crossing the Williamsburg Bridge, and the monster leading it is the Minotaur, forcing Percy toward an immediate new crisis.