Percy Jackson, his friends, and the Olympians fight in a war resembling the original war between the Greek gods and the Titans and in a final battle with the powerful Titan, Kronos. Many fight for Olympus, including the Hunters of Artemis, dryads, satyrs, naiads, and tree nymphs, Chiron's centaur cousins the Party Ponies, and the hellhound Mrs. O'Leary. They must defend Mt. Olympus from Kronos' huge army consisting of rogue half-bloods, dracaena, Hyperboreans, Laestrygonians, drakon, Hyperion, telekhines, Typhon, and hellhounds.