15-year-old Sokka and his 14-year-old sister, Katara, are near a river at the Southern Water Tribe, a small village in the South Pole. While hunting, they discover an iceberg that when broken open shoots a beam of light into the sky. Inside of the iceberg is a 12-year-old boy named Aang and a giant flying bison named Appa. Unknown to them, Aang is the long-lost Avatar — the only person capable of “bending” all 4 elements of Air, Water, Earth and Fire. A century (100 years) has passed since the Fire Nation has declared war on the other 3 nations of Air, Water, and Earth in their attempt to conquer the world.
Zuko is the scarred 16-year-old exiled prince of the Fire Nation on a quest to find the Avatar and bring him to his father, Fire Lord Ozai, so he can regain his honor. Seeing the light that appeared from Aang’s release, Zuko and some Fire Nation soldiers arrive at the Southern Water Tribe to demand the villagers hand over the Avatar. Aang reveals himself and surrenders to Zuko on the condition that he agrees to leave the village alone. On the ship, Aang is tested by Zuko’s paternal uncle Iroh to confirm he is the Avatar. After being informed that he is to be their prisoner for passing the test, Aang escapes using his glider and flies to his flying bison brought by Katara and Sokka. Aang and his new friends visit the Southern Air Temple where they meet a winged lemur, who Aang later names Momo. Aang also learns that he was in the ice for a whole century and that the Fire Nation wiped out all of the Air Nomads, including his guardian, Monk Gyatso. In despair, he enters the Avatar State and finds himself in the Spirit World where he encounters a Dragon Spirit. Katara’s pleas bring Aang back out of the Avatar State.
To seek shelter, Aang’s group arrives at a little Earth Kingdom village controlled by the Fire Nation, but are arrested and taken to a prison for Earthbenders surrounded by earth  because Katara tries to help a young boy escape from Fire Nation soldiers. They incite a rebellion by reminding the disgruntled Earthbenders that Earth was given to them. Aang tells Katara and Sokka that he only knows airbending and must master the other three elements. Katara is given a waterbending scroll that she uses to greatly strengthen and hone her waterbending abilities and to help Aang learn as they make their way to the Northern Water Tribe (where Aang will be able to learn from waterbending masters) and liberate more Earth Kingdom villages in the process, weakening the Fire Nation’s food and water supplies.