The Battle of the Labyrinth camp for the school year. On his fifteenth birthday at the summer's end, Percy receives a visit from his father Poseidon, who gives him a sand dollar, admonishing him to “spend it wisely”. Nico later appears to tell Percy his plan to defeat Luke once and for all. "The Battle of the Labyrinth" was initially referred to as "Percy 4" until the title was officially revealed. The novel was teased by Rick Riordan behind the pages of its predecessor, "The Titan's Curse". It was based on the Greek myth of the labyrinth, where the Minotaur was supposedly kept. In his
The Daedalus Variations original concept of an episode involving alternate realities was a room in Atlantis that shifts into alternate realities. However, the idea had several issues, including the possibility of no Atlantis in one reality, so Robert C. Cooper suggested using the "Daedalus". The final draft of "The Daedalus Variations" was completed on February 11. On February 12, the prosthetics meeting for the episode, as well as "The Seed", "Broken Ties" and "Whispers" took place, which most likely involved the unknown aliens featured from the episode. The appearance of the aliens was revealed in the advertisement for the episode on July 27.