Book 2, Earth, Vol. 4 (episodes 36-40, Plus Bonus Disc)
Avatar Aang continues his quest to master the four elements. He journeys across the Earth Kingdom in search of an Earthbending mentor; he confronts Princess Azula, daughter of firelord Ozai and sister of Prince Zuko. She will stop at nothing to defeat the Avatar. But Aang finds allies along the way, from the swamps of the South to the Earth King's palace.