While traveling through a forest, they were saved by Jet and his freedom fighters, a group of teenage rebels.
Jet quickly caught Katara's attention, but when he tried to kill an old Fire Nation civilian, Sokka stopped him. He warned Aang and Katara that Jet had gone too far, but they did not believe him, so Sokka left. That night, he discovered Jet's plan to blow up a dam and flood a village. Although Jet captured him, Sokka escaped. Aang and Katara caught Jet planting the explosives and realized that he was willing to kill civilians.
Aang fought Jet while Katara froze him to a tree, but the dam was still destroyed. Fortunately, Sokka warned the villagers in time, saving everyone. The group left Jet behind and continued their journey. Later, Aang began having nightmares. Meanwhile, Zuko continued hunting the Avatar. Iroh warned him that a huge storm was coming and urged him to protect the crew first, but Zuko refused.
The group stopped at a market where a fisherman ignored the storm because he needed money, and Sokka joined him for payment. When Aang warned them, the fisherman recognized him as the Avatar and blamed him for abandoning the world for a hundred years. Upset, Aang flew away. Katara found him in a cave, where he explained what had happened a hundred years ago.
The monks had discovered he was the Avatar because of the toys he chose as a child, and they told him before the usual age of sixteen. After that, the other children avoided him, and the monks focused only on his training. Only Monk Gyatso treated him like a normal child. When the elders decided to separate them, Aang ran away on Appa, flew into a storm, and froze himself until Katara and Sokka found him.
On Zuko's ship, Iroh told the crew why Zuko wanted the Avatar so badly. Years ago, Zuko had spoken against a general's plan to sacrifice young soldiers. Fire Lord Ozai saw this as disrespect and forced Zuko into a duel. Zuko refused to fight his father, so Ozai burned his face, gave him his scar, banished him, and said he could only return after finding the Avatar.
Suddenly, the fisherman's wife begged for help, and Katara and Aang rushed after them. Meanwhile, Zuko finally put his crew's safety first and apologized to Iroh. Aang saved Sokka and the fisherman using the Avatar State and briefly met Zuko inside the eye of the storm. Later, Zhao became an admiral and took command of the Yuyan archers, the world's greatest archers, to capture the Avatar.
A mysterious masked stranger watched them. After the storm, Katara and Sokka became seriously ill, so Aang set out to find frozen swamp frogs, the only cure. Instead, Zhao captured him. The masked stranger broke into the fortress and rescued Aang, fighting their way through the soldiers. When they were cornered, the masked man took Aang hostage to force the gates open.
An archer shot off his mask, revealing that he was Zuko. Despite being enemies, Aang saved him. When Zuko woke up, Aang told him that one of his best friends had been from the Fire Nation, and wondered whether they could have been friends too. Aang returned with the frogs to heal Katara and Sokka, while Zuko quietly reflected on his words.
The kids found a damaged ship from their father's fleet, giving Katara hope that he was still alive. Soon, they met Bato from their tribe, who took them to an abbey where nuns made perfume. As he shared stories about their father, Aang began feeling left out. Meanwhile, Zuko hired the bounty hunter June, whose shirshu tracked people by scent, using Katara's necklace.
When Aang received a map showing where Sokka and Katara could meet their father, he hid it, afraid that they would leave him. The next morning, Bato gave Sokka the traditional ice dodging challenge, which he passed with help from his friends. Aang received the mark of trust, but he confessed that he had hidden the map. Feeling betrayed, Katara and Sokka left with Bato, but they soon realized that Aang was already part of their family and that everyone makes mistakes.
Just then, Zuko and June attacked. Aang arrived on Appa and saved everyone. He recovered Katara's necklace while Sokka and Katara blinded the shirshu with perfume, causing it to paralyze its own owners. The trio made up and continued toward the North Pole. The group snuck into a Fire Nation festival to watch firebending. After Aang revealed himself while saving Katara during a show, a mysterious man helped them escape and took him to Jeong Jeong, a firebending master who had deserted the Fire Nation army.
After Avatar Roku appeared, Jeong Jeong reluctantly agreed to train Aang. He taught that fire requires discipline and self-control, but Aang was impatient and accidentally burned Katara's hands. Fortunately, Katara discovered that she could heal injuries with waterbending. Zhao suddenly attacked, revealing that Jeong Jeong had once been his master. While Jeong Jeong told them to flee, Aang stayed behind and tricked Zhao into burning his own ships because of his lack of self-control.
The group escaped safely, and after a long journey they finally reached the Northern Water Tribe, where they received a warm welcome. Aang began training with Master Pakku while Sokka quickly fell for Princess Yue. Katara was denied combat training, because women in the Northern Water Tribe were only allowed to learn healing. During a healing lesson, she discovered that the elderly healer had known her mother.
Meanwhile, Zhao learned that Zuko was the masked man who had freed Aang, and he hired pirates to destroy his ship. That night, they carried out the attack, leaving Iroh devastated. Later, Pakku caught Aang secretly teaching Katara and refused to train him. Katara challenged him to a duel and, despite having become much stronger, was defeated. During the fight, Pakku recognized her necklace, which he had carved years ago for her grandmother, Kanna.
They had once been engaged, but Kanna left the tribe rather than accept an arranged marriage. At the same time, Yue kissed Sokka before revealing that she was already engaged to someone else. In the end, Pakku accepted Katara as his student. Meanwhile, Zuko revealed that he had faked his death with Iroh's help so that he could secretly board Zhao's fleet and continue hunting the Avatar.
Katara's waterbending improved greatly while Aang continued to struggle. While flying with Yue on Appa, Sokka noticed black snow and realized that it was soot, meaning the Fire Nation was close. The city prepared for war. Aang unsuccessfully tried to stop the Fire Nation fleet. That night, Zuko snuck into the city after saying goodbye to Iroh. Since losing his son, Iroh had treated Zuko like family.
The Fire Nation delayed its attack because the full moon strengthened waterbenders. Sokka argued with Yue's arrogant fiancé and was removed from the mission, instead being ordered to protect her. Feeling helpless, Aang followed Yue to the spirit oasis to seek the spirits' help. While he meditated in the spirit world, Zuko attacked. Katara protected Aang's body until sunrise, when Zuko defeated her and kidnapped him.
The kids set out to rescue Aang. In the spirit world, Roku told Aang to find Koh, the face stealer, to locate the moon and ocean spirits, warning him not to show any emotion or Koh would steal his face. On Zhao's flagship, Zhao told Iroh that he planned to kill the moon and ocean spirits to remove waterbending forever.
Iroh warned him not to challenge the spirits, but Zhao ignored him. Koh told Aang that the spirits were the two koi fish living in the oasis. Hei Bai helped Aang return to the real world. Aang woke up tied up by Zuko, but his friends rescued him. Before leaving, Aang saved the unconscious Zuko from freezing. At the oasis, Zhao captured the moon spirit.
The moon turned red, and every waterbender lost their power. Yue revealed that the moon spirit had saved her life as a baby. Iroh warned Zhao that killing it would doom the whole world, but Zhao killed the fish anyway, covering the world in darkness. Furious, Iroh attacked Zhao's soldiers. Aang entered the Avatar State and merged with the ocean spirit, becoming a giant water spirit that destroyed the Fire Nation fleet.
Zuko woke up and fought Zhao. Yue realized that she had to return the life the moon spirit had given her. She sacrificed herself, became the new moon spirit, kissed Sokka goodbye, and restored the moon. The ocean spirit dragged Zhao into the sea. Iroh and Zuko escaped together. Meanwhile, Fire Lord Ozai gave a new mission to Zuko's younger sister. Pakku gave Katara a vial of spirit water while Aang received ancient waterbending scrolls.