As Percy jumps into the Mississippi River from the Gateway Arch, a Nereid, sent by Poseidon, tells Percy to go to Santa Monica. When he arrives, a nereid gives Percy three pearls saying they are gifts from his father, Poseidon. Percy takes the pearls with him to the Underworld. Hades tries to kill Percy, Annabeth, and Grover when they smash the pearls at their feet, the pearls then carry them to the middle of Santa Monica Bay because, as the Nereid said, "What belongs to the sea returns to the sea."