This time, the story tells of three unlikely friends: an amnesiac, an apparent kleptomaniac, and a mechanic, as they are thrown in together on a quest to save Hera, Queen of the gods, before she is lost to the world forever. Riordan set the book two seasons after the events of The Last Olympian (during the winter) so that previous characters could be involved and so readers wouldn't be confused. He says that it was his way of letting his readers "revisit that world in a fresh twist, but also to catch up with Percy, Annabeth, and the rest of the gang from the first series."