Katara and Sokka discover that Aang is the long-lost Avatar and must rescue him when a Firebending prince named Zuko kidnaps him.

Aang is excited about going home for the first time in one hundred years, but he is shocked to find out that the temple is deserted. Aang tells Sokka and Katara about his childhood as they explore the temple, but they soon discover something that Aang never expected. Meanwhile, Zuko must make repairs to his ship and the only way he can do it is to dock his ship at his rival's naval base.

In a nearby Earth Village, the gang meets a teenage earthbender named Haru. This village lives in fear of the Fire Nation, for soldiers there capture any earthbenders they can find.

Aang and friends visit a village being terrorized by an angry spirit. Iroh is captured by Earth Kingdom soldiers.

To contact the spirit of the previous Avatar, Aang must reach a temple in the Fire Nation before the sun sets on the following day. There he will learn what he must do to restore balance to the world. Zuko must defy his banishment to follow Aang.

Aang, Katara and Sokka have run out of money. Katara suggests Sokka get a job, and coincidentally, they meet a fisherman who is looking for someone to help him out with his fishing. But when the fisherman recognizes Aang as the Avatar, he blames Aang's absence for all of the troubles of the last 100 years, and Aang runs away on his glider. Katara follows on Appa, and when she finds him, Aang begins to reveal his life before he was frozen in the iceberg. Meanwhile, Zuko and Lieutenant Jee get into a fight, but Iroh breaks it up. Soon thereafter, the Lieutenant and the rest of the crew gain a newfound respect for their leader after learning of his past.

While Aang, Katara and Sokka are traveling, Sokka gets a fever. Katara and Aang try to help Sokka, when Katara also catches the fever. It's up to Aang to go up on his own to save his two friends. But before he can get the medicine he is captured by the newly promoted Admiral Zhao and put in Zhao's fortress.

When the group tries to help a man who is being attacked by a platypus-bear, they discover that the local town has a fortuneteller named Aunt Wu in it, who has been forecasting the town's fate for years. But when Sokka and Aang discover one of the fortuneteller's most vital predictions is dead wrong, they have to develop a plan to convince the stubborn townspeople that their beloved Aunt Wu was wrong.

When Aang tries to find the north pole, he is found by the north pole instead. As they are taken there, Aang and Katara are eager to find a waterbending master, only to discover that girls are not allowed to learn waterbending.

Zhao begins to launch his attack against the Northern Water Tribe. As the walls of the prestiged city begin to fall, the Avatar taps into the spirit world and seeks the help of one of the oldest spirits, in hopes of saving one of the most prominent areas of the world.

Aang returns from the spirit world to a big surprise. Meanwhile, Zhao and his forces continue to press deeper into the Northern Water Tribe. Iroh makes a powerful stand and Zuko struggles to keep his plan intact.

Plagued with nightmares featuring the devastating power of his Avatar State, Aang and the gang meet an Earth Kingdom general who has big plans for defeating the Fire Nation. Meanwhile, Zuko and Iroh, having survived the failed attack on the North Water Tribe, have a surprise visit from Zuko's sister with seemingly good news.

In search for an Earthbending teacher for Aang, the kids go to an underground Earthbending tournament called Earth Rumble 6, where they encounter Toph, a blind but powerful Earthbending girl. After seeing her unique style of Earthbending, Aang wants Toph to become his teacher, but there are complications with Toph's family.

Toph's instructing abilities come into question when Aang cannot seem to overcome a block that keeps him from earthbending. Sokka gets himself in a jam, while befriending what was, moments before, his next meal, and Iroh and Zuko begin training utilizing new philosophies and methods that originate from the other elements.

Having made it to the outer wall of Ba Sing Se, the kids confront a Fire Nation army that is driving a massive Fire Nation drill, which poses an imminent threat to the last Earth Kingdom stronghold. Meanwhile, Zuko and Iroh make crucial mistakes which begin to attract Jet's suspicions.

Aang travels to the Eastern Air temple to receive guidance from Guru Pathik while Sokka is reunited with his long-lost father. Meanwhile, Azula has something diabolical in store for her enemies in the Earth Kingdom, including Zuko and Iroh.

Everyone races against time to stop Azula's sinister plan. Zuko finds companionship in an unlikely source. Aang's destiny hangs in the balance—and so does Zuko's, as Iroh tells him it's time to make a choice.

Aang awakens to find himself aboard a captured Fire Nation ship with a full head of hair and sustaining serious injuries from the previous battle for Ba Sing Se. At his side are Katara, Sokka, and their father Hakoda who recount the events that led the four to the ship and contemplate their next move. Aang struggles to fight his own desire to face the Fire Lord before he is ready. Meanwhile, Zuko deals with his own issues as he makes his long-awaited journey home, with the fear of his father's rejection hanging over his head.

The day of the eclipse has arrived, and the invasion force gathers together to make last preparations. They infiltrate the island and the battle begins. Meanwhile, Aang searches for the Fire Lord.

As the invasion force fights their way to the Fire Nation capital, the kids help Aang find the Fire Lord in time for the eclipse. Zuko confronts his father with shocking news.

Aang struggles to decide whether or not he has to kill the Fire Lord and, during the night, is drawn toward an island which disappears before morning. Zuko leads the rest of the group to the Earth Kingdom to meet a tracker whom they hope can find Aang. The Fire Lord crowns himself Phoenix King and Aang awakens on the island not knowing where he is.

While on the island, Aang seeks guidance from his past lives, but is not pleased with what he is told. The island, in fact, turns out to be a lion turtle from which Aang is given the guidance he had been seeking. After the tracker is unable to track Aang, the rest of the group decide they must find Iroh. Meanwhile, while tracking down Iroh, the group meets up with The Order of the White Lotus, a group that transcends the division of the four nations.

Sokka, Suki, and Toph try to stop the Fire Nation's air fleet. Meanwhile, Zuko and Azula duel in an Agni Kai and Aang confronts the Fire Lord. On the verge of losing, Aang gets hit in the back of his scar which sends him into the Avatar State.

Aang defeats the Fire Lord by bending the elements within the Fire Lord and removing his firebending abilities. After Zuko is taken down protecting Katara from Azula, Katara joins the fight and manages to restrain Azula. Afterwards, Zuko is crowned Fire Lord and promises a better future for the world, while Aang takes his place as the next Avatar. Katara finally shows her love for Aang as they kiss under the setting sun.