Okay. So Book 1 of Last Airbender was pretty crazy and full of plot twists, but in Book 2, things really get crazy. Aang is running out of time to master all the elements, so someone suggests that instead of mastering the elements, he learns how to trigger the Avatar state. The problem with this is that if he dies in the Avatar state, then the Avatar spirit dies and the cycle ends. If Aang battles the Fire Lord in the Avatar state then, potentially, there will never be another Avatar. Zuko and Iroh are visited by Azula who tells them that they are allowed to return home, but they soon discover that her summons was a trap to imprison them. They escape, but this means that they are both fugitives of the Fire Nation now and can never return home. While on the run, Iroh accidently drinks some poisonous tea, but is helped by a healer named Song. She shows Zuko the effect the war is having on innocent civilians and he experiences some feels!
The gang gets caught in a tunnel called the Cave of Two Lovers, which is bad for them, but also great for the audience because Aang and Katara finally kiss so we’re all thinking: “Hey! Maybe this will alleviate all the awkward sexual tension!” (Spoiler alert: it didn’t). Their torch—literal torch, not metaphorical love torch—burns out, setting off glowing lights on the ceiling that lead them out of the cave and into the city of Omashu…which is now under the control of the Fire Nation. Aang is worried because he can’t find his friend Bumi who was in charge of Omashu. Sokka helps all the citizens escape by pretending they have an illness called pentapox, but the Fire Nation Governor’s son accidentally leaves with the civilians as well. Aang uses this as an opportunity to trade for Bumi’s release, but Bumi tells Aang that he must wait for a more proper time to escape. He then tells Aang to find an Earthbending master who “waits and listens.”
Meanwhile, Zuko has taken on a second identity called the “Blue Spirit,” a disguise he uses to steal food for him and his uncle. When Iroh finds out Zuko is stealing, he becomes angry and Zuko leaves him. He goes to an Earth Kingdom town where he becomes friends with a young boy named Lee who lets Zuko stay with his family. However, once they discover who he really is, they (obviously) make him leave.
Aang is also in the Earth Kingdom looking for an Earthbending teacher. He discovers this teacher who “waits and listens” at an Earthbending competition: a blind Earthbender named Toph (who is such a bad ass). However, her parents won’t let her be Aang’s teacher, so she runs away to join his gang. The group starts getting chased by a mysterious machine that makes it impossible for them to stop for sleep, and this makes them all super angsty, so Aang tries to lure the machine away but he’s stopped by Azula. His friends (plus Zuko and Iroh, who are apparently friends again) show up to take down Azula, but she injures Iroh and escapes.
At an oasis, the group—that no longer includes Iroh and Zuko—meet a professor who tells them about a hidden Spirit Library (aka the library of my dreams) that’s hidden in the desert. Once inside, Sokka discovers some crucial information: the date of an upcoming solar eclipse which will cripple the Fire Nation’s Firebending and potentially end the war (woo!). The spirit guard of the library doesn’t want them to leave with all the information they have discovered and sinks the library into the sand. They escape, but Appa gets kidnapped by Sandbenders. Without him, they have no way of escaping the desert. However, Aang tracks them down and learns that Appa was traded to a merchant in Ba Sing Se (the Earth Kingdom capital), so, of course, they start making their way to the Earth Kingdom.
Zuko and Iroh are also on their way to Ba Sing Se, hoping to start a new life there. Zuko meets Jet and some of the Freedom Fighters (a group of kids dedicated to ending the reign of the Fire Nation) and they begin to bond. However, they soon find out that the Fire Nation is about the send a gigantic drill to destroy the city’s wall. Luckily, Aang and Co. are able to stop the drill in time. Meanwhile, Jet wants to make Zuko a Freedom Fighter, but discovers that he is a Firebender. Unfortunately, while trying to gather evidence of this, he gets himself arrested (It’s not really unfortunate at all. Does anyone actually like Jet? He’s a huge tool.)
Once Aang finally makes it into Ba Sing Se, he tries to tell the Earth King about the solar eclipse, but their tour guide, Joo Dee, won’t let them. They discover that talking about the war is illegal and enforced by the Dai Li (the secret police) and their leader, Long Feng (WHO IS BRAIN WASHING PEOPLE BY THE WAY). Appa and Aang are finally reunited with the help of Zuko (say what?) whose uncle encouraged him to free the bison and give up the Blue Spirit.
Meanwhile, Azula and her friends, while disguised as the Kyoshi warriors, infiltrate the city, those little sneaks.
Aang meets Guru Pathik who can train him to master the Avatar state by unlocking the chakras. He succeeds in unlocking all of them, except the last which requires him to give up all earthly attachments but he’s in love with Katara so he can’t. Elsewhere, Toph invents metal bending, like the gangsta she is.
In the last episode of the season, Zuko prepares to capture the Avatar, but before he can, Azula takes control of the Dai Li (and essentially all of Ba Sing Se) and has Zuko arrested. Iroh tells Zuko that he has to choose between his uncle and his sister. Zuko chooses to fight alongside Azula (stupid). Aang realizes he has to let go of Katara in order to save her, so he does (frown) and enters the Avatar state. While in this state, Azula zaps him with lightning. Iroh helps the gang fight off Azula so that they can escape with Aang’s body. Katara uses spirit water to heal Aang as they flee. They make is out alive, but the Earth Kingdom’s largest city is now under control of the Fire Nation.