The Son of Neptune is the second book in the Heroes of Olympus series, which follows the Percy Jackson and the Olympians series. All of the books follow Greek (and Roman) mythology and tell the story of the modern demi-gods, or half-bloods, the children of a Greek/Roman god and a mortal. They possess some of their goldy parent's mystical powers and abilities and end up having to go on quests to protect the world from compelte destrcution whether it is the Titans trying to reclaim the Gods' power or Gaea, trying to reclaim the earth from the humans.