The Fire Nation conquering Omashu was never going to be a good thing, but it also isn’t much of a simple thing either, and that’s due to King Bumi being a wee bit eccentric and Azula being Azula.
Sneaking into Omashu is actually a little easy if you’re a bender and don’t mind going through the city’s sewers. The real complications come from what’s inside. First, though there is a resistance, they aren’t please with Aang’s buddy Bumi because Bumi surrendered the city without a fight, and he’s still locked up somewhere. As such, the resistance isn’t really interested in rescuing him.
The second complication is Azula is in town, recruiting. She’s trying to put a band together, and while she seems to be the only firebender in the bunch, her two friends are far from helpless. Ty-Lee is a fun-loving free spirit and a talented acrobat, and though Ty-Lee would rather not leave the circus, something about Azula’s attendance and demands of the performers gets her old schoolmate to change her mind about leaving show biz. On the other end of the spectrum is Mai, a rather disaffected and bored young lady, daughter to Omashu’s Fire Nation governor and an expert at throwing bladed weapons or all kinds.
Now, Aang and his friends realize the resistance isn’t going to win anything due to a serious lack of manpower, so the only thing to do is evacuate, oh, everybody, something that’s actually easy to do by faking a plague. Turns out you can walk right out the gate if you look sick enough in a large enough swarm. There’s just one other problem: Mai’s toddler brother Tom-Tom followed Momo out the gate, so they need to return the baby and Aang still wants Bumi back. Fortunately, a trade is offered.
Unfortunately, Aang goes himself and loses his hat, allowing Azula to see exactly who he is, and since the Avatar is worth more than both a toddler and a foolish old man, the deal’s off and the fight is on.
In an interesting turn, Katara proves herself rather formidable and able to take on both of Azula’s new associates until Ty-Lee hits her with some taps that temporarily paralyze her arms. Fortunately, Sokka is up to a rescue with Appa.
As for Aang, he does get Bumi back and eventually manages to lose Azula on Omashu’s sliding mail system when Bumi finally helps…only to find out Bumi doesn’t want to be rescued. See, earthbending is all about patience and finding the right time to strike. He was never helpless. He didn’t surrender. He was waiting. As such, he’s allowing himself to be recaptured and asking Aang to find a new trainer for earthbending, someone who is also very patient and waits for the right time to strike.
That..fits with what I would think the earth should be like. Yes, it can move in sudden, violent actions like earthquakes and landslides, but it’s mostly sedentary. It doesn’t flow freely like water or air, and it’s all violent destruction like fire. It’s mostly strong and steady. I like that characterization.
So, Bumi stays in captivity, Aang and his friends return the baby in secret and move on, and Azula, initially recruiting to find her brother and uncle, now has a third target to bring home.