While Katara herself becomes a great waterbending master, Commander Zhao plans a siege on the Northern Water Tribe. Meanwhile, Sokka's on a mission to stop this siege while Aang tries to buy them some time.
Aang and friends arrive in the Earth Kingdom to begin his training, but a local general convinces Aang that all he needs to do is learn to control his Avatar state. Azula arrives to escort her brother and uncle back to the Fire Nation.
Finding the city of Aang's old friend, King Bumi, captured by the Fire Nation, the heroes hatch a plan to rescue Aang's earthbending teacher. Azula gathers two old friends to help her hunt the Avatar.