Aang and his friends arrive in the Earth Kingdom city of Omashu. Sokka, Azula, Katara and are amazed at the sight of Omashu, noting how they do not have any cities like Omashu back at the South Pole, including having buildings that do not melt in the heat. Zuko and Ozai, on the other hand, were asleep at the back of the saddle.

After two months of traveling, and nearly completing his airbending training, Ozai was now six months pregnant and three months away from his due date.

Aang wanted to get to the city as soon as possible, but Katara stoped him, pointing out, "It could be dangerous if people find out that Ozai is the Avatar and pregnant,", and suggests, "Maybe Auntie Ozai should don a disguise for the time being.".

Using some of Appa's shed fur, Aang puts on a makeshift wig and a fake mustache, adopts an old man voice, and uses as a walking stick. Despite Aang's complaints about the fur being itchy, Sokka and Katara are pleased with his disguise, with Sokka adding that Aang looks just like his and Katara's grandfather. Katara, noting how Aang is technically 112-years-old, points out that the disguise itself is rather fitting. Ozai, Azula, and Zuko just don cloaks.

As they approach the city's walls, Aang remarks, "Omashu is one of the friendliest places in .". However, guards at the city wall are giving a trouble for trying to bring rotten cabbages into the city, and his vegetable-filled cart into the valley below, prompting the dismayed merchant to scream, "No! My cabbages!"

Telling Sokka and Katara to keep smiling, Aang and the group approach the guards, though are immediately halted by one of them levitating a boulder over Aang's head, demanding, "State your business.".

Aang, using his old man-voice, angrily claims, "My business is my own! I ought to bend you over my knee,". When the guard tells him, "Calm down, sir! What is your name?", Aang introduces himself as "Bonzu Pippinpaddleopsicopolis the Third" and claims that Sokka and Katara, the latter of whom introduces herself as "June Pippinpaddleopsicopolis," are his grandchildren while Ozai, Zuko, and Azula were their friends. After eyeing them suspiciously for a moment, the guard tasks "June" with keeping her "grandfather" out of trouble in Omashu and lets them pass. However, when Sokka walks by the guard, the captain stops him, momentarily alarming Team Avatar to have been discovered, though he only wanted to berate Sokka for seemingly not respecting the elderly as he did not carry his grandfather's bag for him. Hearing this, Aang immediately tosses the bag he was carrying to Sokka. As they reach the wall, it is bent open, shocking the siblings with the immensity of the city. Walking through, the gates closing in their wake, Momo, who was hiding in Aang's wig, pokes his ears out, much to the guard captain's surprise. Before he could do anything about it, however, the gate closed and hid the six out of sight.

Aang showed them the , which consists of miles of tubes and chutes that send packages throughout the city via earthbending. He also tells them, "One hundred years in the past, my eccentric childhood friend, , and I would slide down the Omashu delivery system for fun,". Bumi told Aang to always open his brain to the possibilities in life, and Aang affectionately called Bumi a "mad genius".

Aang promised Katara and Sokka that they will go to the once they have a ride down the chutes. They go to the highest point in the city and slide down, almost getting killed by a package of following behind them as they slide. Aang derails them from the chute, and their bin scrapes across the rooftops of several houses. Panicking, they cannot stop and crash into the cabbage merchant's cart, who screams once again in dismay for his ruined cabbages. They are surrounded by guards and taken captive to be punished by the for "vandalism, traveling under false pretenses, and malicious destruction of cabbages."

The king, an aged old man, looks for a while at Aang and, instead of punishment, orders that they shall be thrown a feast, to the surprise of the guards and Team Avatar. At the feast, the king inquires about where Aang came from, to which Aang lies that he came from Kangaroo Island. The king cracks a joke, saying he is heard that place is "really hoppin'", which only Sokka laughs at. Feigning his departure from the table, the king suddenly throws a at Ozai, causing him to catch it with , revealing to everyone that he is the Avatar.

Aang and the others try to leave, but are detained by the guards. The king declares that the Avatar shall face three deadly challenges the next day to win the freedom of himself and his friends, and locks them in a recently refurbished chamber. Ozai looked at Katara and started worrying, "I can't face three deadly challenges! I'm right at the end of my second trimester, entering my third! What if something happens and something happens to my baby?!"

Katara gripped his shoulders and told him to calm down. "Aunt Ozai, you need to calm down. The baby will be fine, you've mastered firebending, and you've almost completed your airbending training. You'll be fine."

The next day, Ozai woke up and found that Azula, Zuko, Sokka, and Katara are missing. The king holds them hostage and promises to return them once the challenges are completed. Ozai threatened the king and demanded, "You return my children and their friends immediately,", but the king brings forth Zuko, Azula, Sokka, and Katara and has rings of placed on their fingers. Known as "creeping crystal", the crystals will grow until they cover the entire body, and only the king can undo the process. For the safety of his family, Ozai agreed to undertake the king's challenges.

For the first challenge, Ozai must retrieve a "lunchbox" key hanging from a chain within a powerful, cascading waterfall. However, it is not as simple as it seems. The force of the water was too powerful for Ozai to simply dive in or approach from below and climb the ladder. Even by using firebending, Ozai couldn't get to the key. The crystal creeps up to cover Zuko, Katara, Azula, and Sokka's arms. Ozai resorted to breaking the tip of a stalagmite off, and, using firebending, shoots it like a dart into the waterfall, breaking the chain and carrying the key to the king, who was watching from a balcony.

For the second challenge, Ozai must return the king's lost pet to him. Outside, Ozai sees a and chases after it, assuming it to be the King's pet, but a large appears and begins to chase Ozai. The rabbit escapes and the monster closes in, but Ozai suddenly has an idea. He turns to face the monster and realizes that this is the real Flopsie. Flopsie picks Aang up tenderly and gives him a huge lick before dropping Ozai and running to the king, who rubs the monster's belly. The children were covered from head to ankle in crystal, and Ozai demands the final challenge begin.

In a large arena, Ozai must battle an opponent. He is allowed to choose which opponent to fight, with the king warning him to choose carefully. He can pick one of two nasty-looking gladiator-like warriors, but he realizes that he can choose to fight the king. Ozai chose the king, who declares he made the wrong choice, removing his robes to reveal a surprisingly muscular physique for such an old man. Ozai recoiled, realizing his mistake. The king claims, "I am the most powerful earthbender you will ever meet,", and began the battle.

The king immediately launches several boulders at Ozai; the Avatar dodges, but the king taunts him for such a predictable firebender tactic. As they fight, the king continues to taunt Ozai for his unwillingness to fight. Eventually, Ozai begins to counter the king. With tremendous effort, the king tears a massive chunk of earth out of the ground and holds it over his head. The king thew the massive mound, but the tornado redirects it back at him. He bisects it neatly in two, but Ozai appears out of the dust and pins the king with his swords.

The king concedes defeat, but before releasing his friends, requires Aang to figure out what his name is. Recalling the point of all the challenges, Aang realizes they all forced him to think differently than he usually would. He realizes who the king is, and calls his old childhood friend Bumi, now the old King of Omashu, a mad genius. The two embrace, and Bumi declares Aang has not changed a bit, literally. Bumi shatters the crystal encasing Sokka, Zuko, Azula, and Katara, and eats a piece, revealing that jennamite is made from rock candy.

Sokka and Katara are surprised to learn that the king is actually Aang's old friend, while Zuko, Azula, and Ozai weren't all that surprised, and question Bumi on why he made Ozai do all those challenges instead of just telling Aang who he really was. Bumi explains that, aside from finding it fun to mess with people, as the Avatar, Ozai has a difficult task to restore balance to the world by defeating . With how much the world has changed in the hundred years that he had been gone, Ozai still has much to learn, and Bumi hopes that when he does, he will think "like a mad genius".

Aang thanked Bumi for all he had done and challenges the king in return. The two of them go sliding down the Omashu delivery system like they used to do a century prior, which results in them crashing into the cabbage merchant's cart, just like Team Avatar did before.