Percy prepares to leave Camp Half-Blood with only basic supplies, while Chiron equips the questers with mortal money, golden drachmas, nectar, and ambrosia. Annabeth brings her invisibility cap, a bronze knife, and an architecture book; Grover packs food and his reed pipes. At the hill, Luke catches up and gives Percy winged shoes from Hermes, but Chiron warns that a son of Poseidon should not travel through the air. Percy gives the shoes to Grover instead, turning them into Grover’s quest item.

Before the group departs, Chiron gives Percy an ordinary pen that transforms into the celestial bronze sword Anaklusmos, or Riptide. Chiron explains that the sword kills monsters but passes harmlessly through mortals, and that the Mist will make mortal witnesses misinterpret supernatural events. Percy tests the pen’s enchantment and learns it always returns to his pocket. Percy then questions Chiron about the immortality of the gods and the earlier age of the Titans, and Chiron warns that Percy may be helping prevent a catastrophic war.

Argus drives Percy, Annabeth, and Grover into Manhattan. During the ride, Annabeth explains that Athena and Poseidon are rivals, which helps explain her friction with Percy. At the bus station, Percy tears down a missing-person flyer with his own picture on it and thinks about his mother. Grover tells Percy that Sally married Gabe because Gabe’s awful human smell masked Percy’s demigod scent from monsters, which reveals that Sally endured Gabe to protect her son. Percy privately admits that his real reason for accepting the quest is to rescue Sally from Hades, even though the Oracle’s prophecy warns that Percy will fail to save what matters most.

While waiting for the bus, Grover senses danger, and once the trio boards, Percy sees Mrs. Dodds arrive with two other old women who are also Furies. The monsters trap the exits, so Annabeth gives Percy her cap and sends him invisible toward safety, but Percy turns back when the Furies attack Annabeth and Grover. Percy causes chaos by grabbing the steering wheel and later the emergency brake, which sends the bus crashing off the road in New Jersey. Outside the bus, Percy reveals himself, uses Riptide to destroy two Furies, and fights Mrs. Dodds while Annabeth and Grover help restrain her. A lightning strike blows apart the bus roof, but Mrs. Dodds survives long enough to call for reinforcements, so the three friends flee into the dark woods.