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.

Aang feels neglected as Katara and Sokka reunite with Bato, an old friend of their father’s from the South Pole. They begin to reminisce on their times in the past while they wait for a message to arrive from their father. Aang believes Katara and Sokka will abandon him and go out to find their father should the message arrive. However, when the messenger gives Aang the message to give to Bato, Aang betrays his friends in a way Katara or Sokka could never imagine. However, when Zuko recruits a bounty hunter named June to track Aang down, his friendship is put to the test as he must deal with the fact that he betrayed his friends while defending himself from yet another fight.

Aang and his friends go to a Fire Nation town so that Aang can witness some firebending, but their plan soon goes awry when it’s discovered that he is the Avatar. Fortunately, he's rescued by an individual who serves a firebending master named Jeong Jeong who has abandoned the Fire Nation, so Aang decides to use this time to attempt to learn firebending. The firebending master, however, seems reluctant to teach Aang.

When Aang and his friends hear rumors about surviving airbenders, they decide to stop by the Northern Air Temple on their way to the North Pole to see for themselves. What they find is a bunch of people who are not airbenders, but have mastered the art of gliding; though this upsets Aang because they have been defacing the temple. However, there was one part of the temple where nobody has been able to enter, and what Aang and his friends discover inside spells oncoming conflict.

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.