Jason wakes to find the Argo II under siege by a violent storm. Rushing to the deck, he finds Leo, Percy, Annabeth, and Piper doing their best to keep the ship afloat. Tired of feeling weak and useless, Jason leaps into action and is relieved that Percy welcomes his help. Percy dives overboard to work from the water, and Jason lassoes the strongest wind spirit, ventus, encasing himself in it, and follows Percy. Jason finds Percy at the bottom of the ocean following a green searchlight. They track it to the ruins of an underground palace, where a 20-foot-tall woman with jellyfish for hair is conjuring the storm above. She introduces herself as Percy’s sister, saying that she wanted to meet him before he died.

They’re in the ruins of Poseidon’s old palace, and the woman is Kymopoleia, a daughter of Poseidon who is banned from her father’s new home. She resents the Romans for not worshipping her and resents her father for having arranged her marriage to the giant Briares against her will. Percy notes that Briares is a friend of his whom he freed from Alcatraz, but Kymopoleia doesn’t appreciate this since she hates her husband.