While at Xin Fu's earthbending tournament, Team Avatar witnesses a display of powerful earthbending by a young blind girl named , who Aang recognizes as the girl from his vision in the spirit swamp. Iroh then teaches Zuko the art of redirecting lightning, a firebending technique he created himself by studying waterbenders. Elsewhere, Azula and her cohorts infiltrate the city, disguised as the Kyoshi Warriors. Aang finds Sokka in danger from a Moose-Lion and is able to save him by firmly standing his ground as an earthbender would. After an intense battle between Team avatar and the Dai Li on the surface, during which Jet is killed by Long Feng, Aang and Appa are finally reunited. He later unwillingly enters a fight with a Boarcupine, and wins but is badly wounded.
The season's executive producers and co-creators are Michael Dante DiMartino and Bryan Konietzko, who worked alongside episode director and co-producer Aaron Ehasz. Aang nearly destroys the base in anger but is then told by Avatar Roku that if he is killed in his Avatar State the Avatar Spirit will cease to exist, bringing to an end the cycle of reincarnation which preserves the Avatar as a force for balance in the world. But General Fong, inspired by Aang's battle-determining actions during the Siege of the North, suggests that Aang defeat the Fire Lord and end the war immediately by triggering the Avatar State. After many failed attempts, General Fong finally succeeds in triggering the Avatar State by faking 's death. The season was created and produced by and , and starred , , , Jessie Flower, , , and as the main character voices. He explains that all beings are connected, as the swamp is , and the visions are of people they have met or will meet.
Xin Fu kidnaps Aang and Toph thinking he was cheated. Meanwhile , disgusted with having to live as a beggar, dons the mask of the Blue Spirit once again. Battling against Azula, Mai, Ty Lee, and contingent of firebending soldiers, Aang and the group succeed in stopping and destroying the drill from the inside. There is a genuine classic feel to the series, which uses actual Asian culture and lore as its base. Aang is pardoned after he defeats a group of Fire Nation soldiers that attack the village, and the town changes the anti-Avatar celebration to a pro-Avatar celebration.
Elsewhere, Iroh reveals a mysterious association with some form of secret society when he uses a White Lotus tile as an opening in a match of Pai Sho, his favorite game. Katara uses a vial of spirit water earlier given to her from the pool of the spirits after the Siege of the North in order to save Aang as the team, with a deposed Earth King Kuei in tow, flees from Ba Sing Se, now in the hands of the Fire Nation after a century of resistance. They begin to see unique illusions in the swamp: Sokka sees Princess Yue, Katara sees her dead mother, and Aang sees a mysterious girl and a flying boar. The boxset was released on July 20, 2009. The move functions as some sort of message to his opponent, who then helps protect Iroh and Zuko from a Fire Nation search.
After a long trek and much hardship in the desert, tracks down the sandbenders who stole Appa, and learns that Appa was traded to a merchant and is likely in Ba Sing Se, the imposing capital city of the Earth Kingdom. Aang and grow even closer as they discover the origins of the cave, which includes the tombs of the first two earthbenders. Note: This episode won a Humane Society award for its portrayal of the mistreatment of animals. Pursuing both Zuko and Aang is , Zuko's younger sister. They are assigned a liaison, an uncomfortably cheerful young woman named Joo Dee, who indirectly makes it clear to them that any mention of the war is forbidden within the walls of the city, one of many disturbing rules they begin to encounter that are enforced by the Dai Li, the secret police of Ba Sing Se, and their corrupt leader, Long Feng, who appears to know something about Appa. Meanwhile, wishes to recruit Zuko for his Freedom Fighters, but then learns that Zuko and Iroh are firebenders after deducing that Iroh used firebending to warm up a lukewarm cup of tea.
The group finally makes it to Ba Sing Se only to find the Fire Nation is about to send a gigantic drill to penetrate the titanic outermost walls of the capital region, which have protected the people within, including the Earth Kingdom leadership, form more than a century of Fire Nation assault. However, several new characters appear: Jessie Flower voices , voices , voices Mai, voices Ty Lee, and voices Long Feng. However, with encouragement from his uncle, Zuko decides to free the sky-bison and give up the Blue Spirit alter-ego forever. Completely dispirited, confused, and longing for Aang, Appa returns to his childhood home at the Eastern Air Temple, where he discovers a mysterious guru has taken residence in the ruins. Elsewhere, Zuko discovers that Aang is in the city and sets out in the disguise of the Blue Spirit to find him, and believes he has hit on a winning strategy when he discovers the imprisoned Appa.
Aang manages to rescue Bumi after a fight with Azula, but Bumi allows himself to be recaptured, saying that the proper time for his escape has not arrived and that he will wait out his capture a little longer so as to catch the Fire Nation unawares at the most beneficial moment. Upon hearing that Appa was muzzled, Aang becomes so angry and upset that he enters the Avatar State, almost wiping out the sandbenders, but is eventually calmed by Katara. Toph blames Appa for the chase and the group realize that she is correct: they are being tracked because Appa is shedding. However, they soon discover that the protocols and bureaucracy of the royal court and aristocracy surrounding the Earth King keep them perpetually stalled from making contact with him. The spirit of the library, Wan Shi Tong, refuses to allow them to leave with the knowledge and sinks the library into the sand.
They are attacked by a giant sea serpent, but ward it off and make it past. Rotten Tomatoes gave it an 87% fresh rating in 2008. Appa is forced to flee at Suki's urging, lest he be hurt in the ensuing battle between Azula's forces and the Kyoshi Warriors. They find Smellerbee and Longshot and realize Jet was brainwashed by the Dai Li. Almost at the point of true enlightenment, Aang sees a vision of impending danger for Katara and retreats from disattachment, instantly deciding to return to her and protect her at all costs, even though Guru Pathik warns that this may leave Aang's final chakra inaccessible, compromising his ability to safely and reliably access the Avatar State at all.