Tenzin, Jinora, and Team Avatar travel toward Ba Sing Se in order to find the new airbenders. Stopping at various villages along the way, they hope to recruit them in order to rebuild the Air Nation, though with little success as they were only able to convince a young boy named Kai to join them. Meanwhile, Zaheer travels the four nations to free his fellow criminals from their prison. After freeing Ghazan and Ming-Hua, they set course for the Northern Water Tribe to free their last member, P'Li. Upon learning of their escape, Lord Zuko sets course for the Northern Water Tribe himself in an attempt to stop them.

Team Avatar arrives in Ba Sing Se. While Korra has an audience with the Earth Queen, the others notice that Kai has gone missing, prompting Mako and Bolin to go look for him. They track him down, but he manages to shake them in the monorail, which takes the brothers to the Lower Ring, where they eventually run into their family from their father's side. Meanwhile, Korra and Asami set course for a small village to collect taxes as a favor to the Queen. After getting her money, the Queen brushes off Korra's request for help in tracking down the airbenders, leaving the Avatar to storm out of the palace. In the city, Kai found himself arrested by the Dai Li and subsequently conscripted in the Earth Queen's first airbending regiment.

Lord Zuko, Tonraq, Desna, and Eska try to prevent Zaheer from freeing the last prisoner, P'Li, while Korra discovers that the Earth Queen is forcing all the airbenders in Ba Sing Se to join her army. Team Avatar thus devises a plan to free them from the monarch's captivity.

Despite Bumi's bad attitude, Tenzin attempts to train the new members of the Air Nation with little success. Things become more complicated for the airbending master as Jinora, with Kai's influence, begins to exert her independence and demand her airbending tattoos. The new airbenders are tested when they are forced to face a group of bison rustlers who have taken Jinora and Kai along with several bison calves.

Mako and Bolin deliver an ominous message from Zaheer.

When other plans fail, Korra suggests a brave idea to take on the Red Lotus and save the Air Nation.

Korra battles Zaheer, while Bolin and Mako duel Ghazan and Ming-Hua. The captive members of the Air Nation escape and band together to help Korra.

It's been three years since Zaheer poisoned Korra and the members of Team Avatar have moved on with their lives; Kai and Opal help a struggling Earth Kingdom town.