Percy tells Annabeth and Tyson about Hermes secretly giving him supplies and encouraging him to go after Grover. Annabeth immediately insists on joining the quest, but she panics at the idea of taking Tyson because they are heading toward Polyphemus, another Cyclops. Percy feels embarrassed and uncertain about Tyson coming, yet he decides Tyson cannot be left behind to face Tantalus’s punishment, so all three leave together as harpies close in.

Percy calls on Poseidon for help, and three hippocampi rise from the sea. The trio escapes Camp Half-Blood on the sea-horses and races after the cruise ship, the Princess Andromeda. When they reach the hull, the hippocampi bring them to a service ladder; Tyson sadly says goodbye to his mount, whom he names Rainbow, and Annabeth forces open a maintenance entrance so they can sneak aboard.

Inside, the ship feels wrong. The corridors and decks appear empty, Tyson smells monsters, and Percy senses a familiar danger even though they find no one at first. The trio eventually discovers an open luxury suite with food, drinks, and a welcome note, and Hermes’s duffel bags turn out to contain money, clothes, rations, Annabeth’s invisibility cap, and Tyson’s tools. Annabeth warns Percy not to trust anything on the ship, and they lock themselves in separate rooms to rest.

While sleeping, Percy dreams first of Tartarus, where Kronos mocks Percy’s loyalty to the gods and predicts another failure. The dream then shifts to Grover in Polyphemus’s cave, still disguised as the Cyclops’s bride. Grover keeps himself alive by undoing and reweaving his bridal train, but Polyphemus grows impatient, and Grover manages to bargain for only seven more days. The dream confirms that Grover is in immediate danger and time is running out.

In the morning, a cheerful intercom announcement includes “disemboweling practice,” confirming the ship is no normal cruise. Percy, Annabeth, and Tyson now see mortal passengers and crew walking around in a trance, repeating canned lines and ignoring the monsters among them, including a hellhound at the buffet. Hiding in a restroom, the trio overhears reptilian voices saying “six more joined yesterday,” then hears Luke and a companion named Agrius discussing bait and a mysterious casket in the admiralty suite. Because Luke is clearly using the ship for a larger plot, Percy and Annabeth decide they cannot simply escape; they must stay and investigate.