Before the quest begins, Percy dreams of Luke aboard the Princess Andromeda, kneeling before Kronos’s golden sarcophagus. Luke reports that Camp Half-Blood is sending a quest and that Kronos’s bargain is almost complete. Kronos insists he will personally lead the invasion through the Labyrinth once they can navigate it, and he says one more heart must join his cause before he fully rises from Tartarus.

Kronos reminds Luke of his oath and of Backbiter, the sword that proves Luke’s pledge. Kelli the empousa arrives to report that the advance team is ready, but she senses Percy watching through the dream and attacks, waking Percy. Percy realizes Luke’s army is nearly prepared to invade Camp Half-Blood.

Awake in the Poseidon cabin, Percy sees the saltwater fountain glowing and asks it to show Nico di Angelo. The vision reveals Nico in a graveyard using Coke and Happy Meals as offerings to summon the dead, while an unnamed ghost advisor pushes him to ask about exchanging souls. Nico summons Theseus, who warns him not to try recovering Bianca and says the Labyrinth can only be survived with guidance like the mortal princess who once helped him.

When Nico asks whether a soul can be exchanged for a soul, Theseus confirms it but becomes frightened because a powerful being has sensed Nico’s summoning. The fountain shakes violently as the ghostly vision grows dangerous, so Percy destroys the fountain with Riptide to stop it. Tyson finds Percy in the morning beside the shattered remains.

At dawn, Annabeth, Percy, Grover, and Tyson gather at Zeus’s Fist while Chiron strengthens defenses around the Labyrinth entrance. Percy privately tells Chiron about the dream of Luke and Kronos. Chiron fears Kronos wants Daedalus not only to guide the army but possibly to build him a new body, and Percy realizes they must reach Daedalus first.

Percy also tells Chiron that Juniper saw Quintus near the entrance, and Chiron admits he already suspects Quintus but prefers to keep him close. Percy withholds the truth about Nico being a son of Hades, deciding he must find Nico himself. After farewells, the four questers descend into the Labyrinth.