Percy falls from the Arch expecting to die, but the Mississippi breaks his fall without hurting him. On the riverbed, Percy realizes he can breathe underwater, stay dry, and even use fire while submerged. The Chimera's poison is gone, which confirms that Poseidon has protected him, but Percy feels ashamed that he could not defeat the monster or save everyone on his own.

As Percy struggles with fear and self-doubt, he hears a woman's voice urging him to take back Riptide. A ghostly water-messenger appears and tells Percy that his mother's fate is not hopeless, but before entering the Underworld he must go to Santa Monica because it is Poseidon's will. She also warns Percy not to trust "the gifts," but vanishes before she can explain, leaving Percy with a new destination and a troubling mystery.

Percy rises from the river near the crowded disaster scene and learns that there were survivors from the Arch. News reporters begin describing an adolescent boy as the likely cause of the explosion, and eyewitness accounts point toward Percy. When Percy reunites with Grover and Annabeth, he explains the Chimera attack, his miraculous survival, and the water-messenger's instructions.

The situation worsens when a television report identifies Percy by name and links him to the New Jersey bus incident as well, turning him into a wanted suspect traveling west. Realizing the police and media are closing in, Percy, Annabeth, and Grover hide from the crowd and make escaping St. Louis their first priority. They reach the Amtrak station without being caught and board a train for Denver as night falls.