Before Aang completely lost control, Katara calmed him down. To reach Ba Sing Se, the group had to cross the Serpent's Pass. Refugees told them that boats were safer. Meanwhile, Jet recruited Zuko and Iroh to steal food from the military, because they were tired of living as refugees. The group struggled to board a boat, but Toph got tickets using her family's seal.
Sokka reunited with Suki. When a pregnant refugee lost her passport, Aang led everyone through the Serpent's Pass instead. During the journey, Katara noticed that Aang had changed since losing Appa, while Sokka felt awkward around Suki after everything with Yue. A giant sea serpent attacked, and Toph nearly drowned. Suki saved her, and Aang defeated the giant sea serpent. They reached the other side, where the woman gave birth.
Seeing the baby gave Aang hope again, so they named the child Hope. Sokka kissed Suki goodbye, and when the group reached Ba Sing Se, they saw a giant drill attacking the city. Azula, Mai, and Ty Lee were inside the giant drill. Ty Lee defeated earthbenders by blocking their chi. Sokka came up with a plan to destroy the drill from the inside before it broke through Ba Sing Se's wall.
Meanwhile, Jet asked Zuko to join the freedom fighters. Zuko refused, but Jet grew suspicious after seeing Iroh heat his tea with firebending. Aang, Katara, and Sokka snuck inside the drill while Toph slowed it from outside. They destroyed its support columns one by one until Azula, Mai, and Ty Lee stopped them. Katara and Sokka blocked the sludge pipes, causing pressure to build.
Aang defeated Azula in battle. The drill exploded and Ba Sing Se was saved. Meanwhile, Zuko and Iroh entered the city by train while Jet secretly watched them. The group finally reached Ba Sing Se, hoping to find Appa. They were welcomed by Joo Dee, a guide with an unsettling smile. During the tour, they noticed that nobody was allowed to talk about the war or meet the Earth King.
Meanwhile, Zuko and Iroh worked at a tea shop while Jet secretly watched them. Tired of getting nowhere, the kids snuck into the palace. During a party, Long Feng explained that talking about the war was forbidden to keep the people believing that there was peace. He warned them to stop searching, or they would never find Appa. Jet fought Zuko, but the Dai Li captured Jet and brainwashed him into forgetting about the firebenders.
Aang and Katara put up posters around the city to find Appa. Joo Dee returned and warned them to stop searching, showing that she had been brainwashed. Long Feng ordered her to report to Lake Laogai. Meanwhile, Iroh was offered his own tea shop in the upper ring. Zuko found one of Aang's posters, but Iroh told him to let go of the Avatar if he wanted true freedom.
At the same time, Jet appeared and offered to help the group. Katara did not trust him, but Toph said that he was telling the truth. They arrived where Appa was being held, but he had already been transported to Lake Laogai, so they planned to rescue him. They met Jet's friends and learned that he had been brainwashed. Their search led them to a hidden base beneath Lake Laogai.
Zuko put on the mask once again and interrogated a Dai Li agent. The kids entered the underground base and fought Long Feng. Long Feng forced Jet to attack Aang, but Aang's words restored Jet's memories. Jet then attacked Long Feng, but he was badly injured, forcing Long Feng to retreat. Zuko found Appa, and Iroh asked what he planned to do, pointing out that he never thought things through.
Even so, Zuko set Appa free. As the Dai Li attacked, Appa rescued everyone, and the group was finally reunited. The group had to warn the Earth King about the war and the solar eclipse. They fought through the palace guards until they reached him. Long Feng tried to lie, but Aang revealed everything and proved that the war was real by showing the destroyed drill.
The Earth King arrested Long Feng. Meanwhile, Zuko became seriously ill because of his inner conflict. Iroh called it a spiritual transformation. The kids finally received the letters Long Feng had hidden from them. Toph could meet her mother. Aang was invited to the Eastern Air Temple. And Katara and Sokka could reunite with their father. The group split up. Katara stayed with the Earth King to prepare the invasion while Aang traveled to learn the Avatar State.
Aang almost confessed his feelings before they left, but Sokka interrupted. Meanwhile, the Dai Li stayed loyal to Long Feng. Master Yu and Xin Fu captured Toph. Azula secretly replaced the Kyoshi Warriors and reached the Earth King. Zuko recovered and happily helped Iroh run the tea shop. Sokka reunited with his father after a long time. Toph was trapped inside a metal cage while Master Yu mocked her, saying that earthbenders could not bend metal.
Aang met Guru Pathik, who taught him to unlock his seven chakras so that he could fully control the Avatar State. To do that, Aang had to let go of fear, guilt, and other emotions. Meanwhile, Azula continued pretending to be a Kyoshi Warrior while Katara prepared the invasion with the Earth Kingdom. Later, the Dai Li heard that the Kyoshi Warriors were from the Fire Nation, but it was all part of Azula's plan.
Katara spotted Zuko and Iroh at the tea shop and went to warn the king, but Azula captured her. Aang saw this in a vision before opening his final chakra. The guru warned him that if he left now, he might never master the Avatar State, but Aang went anyway. Toph discovered metalbending, escaped her prison, and proved that no earthbender was stronger than her.
Aang picked up Sokka and headed back. Meanwhile, the Dai Li arrested Azula and brought her to Long Feng, who offered her a deal: the Avatar, in exchange for control of Ba Sing Se. The group went to rescue Katara. Zuko and Iroh met Azula, who was preparing a coup. Iroh escaped, but Zuko was locked up with Katara. They argued at first, but after talking about losing their mothers, they began to understand each other.
Aang and the others met Iroh, who told them that Zuko was trapped beneath the palace. They decided to work together. The coup began, and Sokka and Toph ran into Mai. Meanwhile, Azula threatened the Earth King, and they were captured. Aang and Iroh reached the prison just as Azula attacked. Zuko had to choose between Azula and Iroh. While Aang and Katara fought Azula, Zuko betrayed Iroh and joined his sister.
Meanwhile, Sokka, Toph, and the king escaped. Outnumbered, Aang entered the Avatar State and let go of his feelings for Katara. Before he could win, Azula struck him with lightning, killing him. Iroh helped them escape. Ba Sing Se fell to the Fire Nation. And although Katara healed Aang with spirit water, something blocked his Avatar powers. Aang woke up on a Fire Nation ship with hair, after sleeping for several weeks.
At first he panicked, but he learned that the ship belonged to Katara's father and his allies. Meanwhile, Zuko returned home after nearly three years and worried about facing his father. Mai comforted him with a kiss. Later, while healing, Aang realized that he had died and that Katara had saved his life. At the Fire Nation capital, Azula and Zuko were welcomed as heroes after their victory at Ba Sing Se.
Meanwhile, everyone believed that the Avatar had died, so the group planned to invade the Fire Nation during the solar eclipse. However, Aang was horrified to learn that the world thought he was dead. Soon, a Fire Nation ship approached them. They tried to fool the enemy, but they noticed inconsistencies and prepared to sink their ship. Toph overheard their plan, and a battle broke out.
Just in time, a giant sea monster attacked the enemy vessel, allowing them to escape. Feeling guilty for failing everyone, Aang ran away. Katara broke down while talking to her father and admitted that she had missed him ever since he left. Zuko met Fire Lord Ozai for the first time in three years. Ozai praised him for killing the Avatar.
When Zuko asked Azula why she had given him the credit, she explained that if Aang was alive, Zuko would take the blame. Meanwhile, Aang was caught in a storm while traveling alone. Avatar Roku told him not to blame himself, and Princess Yue's spirit guided him safely to shore. He regained his confidence, reunited with his friends on Crescent Island, and left his old glider behind.