While traveling towards the North Pole, the group almost gets captured by the Fire Nation. However, when a charismatic young man and his band of rebels attack the Fire Nation camp and rescue them, they learn that they are trying to resist the Fire Nation’s motives to expand their territory. Katara and Aang really enjoy their time with the band of rebels, but Sokka soon discovers that they aren’t as noble as meets the eye.

When Aang and the gang meet up with a group of refugees, they tell the gang where they can get on a ferry to Ba Sing Se. But after a series of events they have to take a deadly route called the serpent's pass with the help of an old friend, Suki. Meanwhile, Zuko and Iroh meet up with a boy named Jet and his freedom fighters.

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.

Having finally made it into Ba Sing Se, the kids are given a house in the upper ring. The kids are anxious to tell the Earth King their plan but there are complications. Meanwhile, still convinced that Iroh and Zuko may be Fire Nation, Jet decides to take matters into his own hands and do whatever it takes to get the refugees to reveal their true nature.

Aang and his friends continue to search for Appa and, unbeknownst to them, they aren't the only ones looking for him. During their search, the kids meet up with Jet, whom they are understandably reluctant to trust. The kids soon realize that the Dai Li are doing their best to thwart the kids' efforts to find Appa. Meanwhile, Iroh is offered his own tea shop in the upper ring, and Zuko discovers the avatar is in the city.