'Legend of Korra' Season 2 a go; Book 2 will be called 'Spirit,' reveals Comic-Con 2012 panel
Now the show is for sure going to return for Season 2, divided into two parts (Book 3 and Book 4). Creator Bryan Konietzko confirmed at Comic-Con 2012 that the four books will be split over 52 total episodes. Book 2 will be called "Spirit" and will take place six months after Book 1.
Additionally, the Comic-Con panel revealed that in Book 2, the show will visit the spirit world and there will be two "very special episodes" in the middle of the season that will explore the mythology of the spirits and the Avatar.