After The Last Olympian, the next time Percy is seen is in The Son of Neptune, the second book in the sequel series The Heroes of Olympus. He is suffering from amnesia and slowly struggles to regain his memory over the course of the novel. For a while in the book he cannot remember anything other than Annabeth Chase, his long-time friend. He arrives at a Roman establishment called Camp Jupiter, and is elected praetor as a result of the help he offers them on a quest. During the remaining three books in the third-person his character develops significantly. He develops an irrational fear of drowning; is humbled by weakening sword-fighting skills; and expresses a new tendency to make ambiguous moral choices in defense of his friends and family. One of the character's darkest moments comes in The House of Hades, when Percy discovers that he can control the water in a person's body, and uses it to torture the goddess Akhlys. Percy's girlfriend Annabeth Chase is present and brings him to his senses, but remains haunted by his readiness to use that new power.