With the Fire Nation moving toward war against the other tribes, a young apprentice named Aang must leave his home at the Southern Air Temple to embrace his destiny as the Avatar – and hopefully save the world.
Katara convinces her brother to help Aang seek the wisdom of Kyoshi, a former Avatar, on an isolated island – where Sokka falls for the village guardian. Meanwhile Prince Zuko's arrival inadvertently tips off a fellow Fire Tribe commander that the Avatar may be nearby.
Aang, Katara, and Sokka arrive at the last great city of Earth Nation, where Aang determines to help protect the people from Fire Nation attacks. While Zuko pursues the airbender to the mountain city, back home his sister moves to secure her own power.
A prisoner of Earth Nation inside Omashu, Aang discovers that their ruler is an old friend of his – a man intent on putting him to the test. While Sokka and Katara enter the tunnels to search for a way to help their friend, Prince Zuko infiltrates the city to rescue his uncle.
Aang and his friends discover a forest ravaged by the Fire Nation and a tiny community living on the edge of a crack between the natural world and the spirit world. Zuko and Iroh enlist the aid of a dangerous bounty hunter.
Aang enters the enemy's lair when he visits the Fire Temple, seeking help from the spirit of Avatar Roku – only to fall afoul of Prince Zuko's bounty hunter. Zuko remembers the events that led him to be exiled by his father.
Aang and his friends arrive at the Northern Water Tribe, where Sokka makes a personal connection with Princess Yue ... and Katara learns that her kindred have old-fashioned ideas about women waterbenders. Elsewhere Azula pushes back against her father, Fire Lord Ozai, and Zuko finds himself a target.
As the Fire Nation fleet draws near the city of Agna Qel'a, Aang, Sokka, and Kitara help the people prepare for war – and Admiral Zhao targets the Moon Spirit itself.
