Aang discovers a secret Fire Nation invention heading straight for Ba Sing Se and must stop it before it destroys the great wall that protects the city from invasion.
8.4
"Great"
Aang warns the commander of Ba Sing Se's Outer Wall, General Sung about the Fire Nation drill headed straight for his city, but the general claims that Aang's help will not be needed; informing Aang that he's sent a group of elite Earthbenders, called the Terra Team, to stop the drill. Mai and Ty Lee, however, quickly disposes of them, striking their pressure points to paralyze them and shooting them with shuriken.
Now realizing the vulnerability of his position, Sung begs for Aang's help. Aang needs to figure out a way to stop the drill, and immediately looks to Sokka for ideas.
Meanwhile, Zuko and Iroh have to get past another clerk, in order to get inside the city, which Iroh accomplishes with a little buttering up. Jet, in the meantime, is looking to recruit Zuko into the Freedom Fighters.
Later, Katara is checking out the injuries received by the Terra Team. After one of the paralyzed Earthbenders tells them that a girl blocked his chi channels and cartwheeled away, Katara recognized her quickly as Ty Lee. Katara's words about how Ty Lee fights gives Sokka an idea to infiltrate the machine and destroy it from the inside, by hitting its pressure points. Toph creates a dust cloud, giving them some cover, then bends them a tunnel to get under the machine. Aang, Katara, Momo and Sokka get inside, but Toph refuses, preferring to try to slow the drill from the outside.
Inside, the gang manages to steal the schematics from an engineer, and figures out an idea to cut through the supports holding the machine together.
Back in the city, Iroh buys a cup of tea from a vendor, only to find out that it's cold. Jet tries to talk Zuko into joining him, but the prince naturally refuses. Zuko turns back to Iroh and find that he used Firebending to heat up his tea. Zuko chastises his uncle for possibly blowing their cover and knocks the tea out of his hand, but it's too late, as Jet has also seen the steam rising from his cup, and starts to suspect the pair as Firebenders.
Inside the Drill, Aang and Katara use Waterbending to saw through a massive support beam, with Sokka "cheering" them on. They cut through the beam with much effort, but it's not enough. Unfortunately, the Drill has just reached the wall. Aang, remembering some of Toph's teaching, comes upon a better idea. Instead of trying to cut completely through a few beams, they only cut partially through many of them. Aang is then to deliver the final blow from above, to bring the entire machine down.
Unfortunately, their previous actions are discovered, and Azula, Mai, and Ty Lee quickly dispatch themselves to take care of them, and the group splits up to escape. Azula goes after Aang and Momo, sending Ty Lee and Mai after the other two. Sokka and Katara escape through a slurry pipeline, a pipe containing rock, sand and water from the drill. Mai refuses to jump into the "Wall-sludge juice," but Ty Lee quickly goes after them.
Katara and Sokka are carried out through the rear of the drill, Ty Lee following soon after. Katara, however, quickly Waterbends the slurry and Ty Lee right back up the pipe, keeping her from attacking them. Aang starts trying to cut a weak point to strike, but is hampered by the panicked efforts of General Sung, who is ordering his troops to continually drop boulders on the drill, to no effect.
At the rear of the drill, Sokka is still cheering his sister on as she Waterbends. Toph shows up, offering some help. As the mud is partially Earth, she lends her abilities to Katara's shoving the slurry (and Ty Lee) all the way back up the pipes.
Topside, Aang is confronted by Azula, who wastes no time in engaging him, even through a rain of falling boulders. Aang fights her off with both water and Earthbending, but gets knocked out by a fire blast just as the Drill breaches the Outer Wall. Azula pins Aang against the wall to finish him off, but Aang recovers, creating a stone hand around his arm to push her away. Before they can begin round two, however, the slurry, backed up by Katara and Toph, overflows the drill, sending a wave of mud over them both. Azula looses her footing and goes slipping into Aang, slamming them both against the wall. They go sliding off opposite sides, Momo helping Aang recover and get himself back up to the top. Using a rock "helpfully" dropped by Sung's men, Aang shapes it into a wedge, placing it right on top of the weak spot. He then runs at full speed up the wall, ultilizing the air scooter, going as high as he can before dropping back down onto the spike of rock. Azula, in a last attempt, shoots a blast of fire towards Aang but misses as he pounds into the shaped rock. The resulting shockwave blows Azula off of the drill, and dislodges many of the machine's weakened supports. The strain of the impact, as well as the pressure of the slurry, is too much for the drill, which collapses into a muddy pile of scrap.
Back at the city dock, Jet makes the realization that Zuko and Iroh are Firebenders, and seeks to confront them on a subway train, the same one Ying and Tahn are also riding on.