Book Two: Earth (土) is the title of the second season of Avatar: The Last Airbender, created by Michael Dante DiMartino and Bryan Konietzko, and the sequel to Book One: Water. The title refers to the Avatar Cycle: water, earth, fire, and air, and the story of Aang learning earthbending under the tutelage of Toph Beifong is a primary focus during this season. In the iTunes release of Book Two, the episodes "The Serpent's Pass" and "The Drill" are combined into one episode titled "The Secret of the Fire Nation".