The Mysterious Fifteenth Olympian

Percy was betrayed 1,000 years ago and thrown aside and thought to be dead. But ten years after Percy's disappearance Lady Chaos comes to them with her Right-Hand Man Vapour Stormbringer, part Cyborg and says he will be their Fifteenth Member and their advisor. But his identity will be known to none. But one. He becomes the Guardian of the Hunt, which they don't like, but one…