The episode begins with Fire Nation tanks moving towards the wall with the drill close behind. Several segments of the drill then extend out making the drill even larger. Steam comes out of pipes and spikes lodge into the ground around the drill. The command module then rises up into the sky attached to the drill like an antenna. Inside the command module is Mai, Ty Lee, Azula, War Minister Ching, and several fire nation soldiers operating the drill. War Minister Ching is bragging about the drill and how it will defeat Ba Sing Se. He says, "Nothing can stop us." Ty Lee then questions whether the earthbenders in the drill's way will stop it. Ching then replies, "The drill's metal shell is impervious to any earthbending attack." and hits the periscope Ty Lee was looking through. Azula doubts Ching and sends Mai and Ty Lee to take out the earthbenders. Mai sighs, "Finally, something to do." Then we see the family Toph, Katara, and Sokka are leading to Ba Sing Se with their new born baby: Hope. Aang flies down on his glider with Momo and lands in front of them. Katara asks what he's doing there. Aang answers Katara and then Toph and Aang are earthbending everyone up the wall. Sokka asks, "Now, what's so big that Appa has to wait?" Aang says, "That." The drill is shown briefly and then everyone is on top of the wall looking down at it with horror. The mother says that they're finally there and that no one is safe. Earthbender soldiers then ask what they are doing there. Aang says that he is the Avatar and asks them to take him to their leader. The general says that their help is not needed and goes on about how the wall is impenetrable. Toph says that the Dragon of the West(Iroh) got in and the general responds saying that he was quickly removed. He makes a joke about the meaning of the word Ba Sing Se. Toph says that there is still the drill. The general says he has sent out a team of Earthbenders called the Tera Team. Sokka comments on the name being catchy. The Terra Team knocks one of the Fire Nation tanks into the air and out of their way. They bend earth spike-like columns to the drill from the ground. The drill extends again and the columns crumble. They all create earth shields protecting them from Mai's daggers. Ty Lee and Mai slide down the drill's side. Ty Lee swings off a rope onto the ground. She deftly takes out all the earthbenders in seconds. Ty Lee is standing over all the defeated benders. The general sees their defeat and exclaims, "We're doomed!" Sokka slaps him and tells him to get a hold of himself. The general apologizes. Toph asks him if he wants their help again. He turns to Aang and says," Yes, please." Katara, Toph, and Aang all look at Sokka for a plan. Iroh and Zuko are at the underground ferries. The ticket lady says their names and looks at them suspiciously. Iroh corrects her on the pronunciation of their names and she gets mad and asks him if he's telling her how to do her job. Then Iroh compliments her and says she's pretty. She likes it and compliments him back. The ticket lady stamps their tickets and welcomes them to Ba Sing Se. Zuko snatches his ticket out of Iroh's hand and says,"I'm gonna forget I saw that." Jet and Smellerbee talk about Lee (Zuko) joining the new Freedom Fighters. Smellerbee doesn't like the idea. Katara is using her healing powers on one of the Earthbenders that was attacked by Mai and Ty Lee. The general asks her what is wrong with him. She tells him that the earthbenders chi is blocked. Katara asks the earthbender who injured him and from the description Katara knows that it's Ty Lee. She is talking about Ty Lee and says, "it's like she takes you down from the inside." Sokka face lights up and he waves his arms in excitement. Sokka says, "What you just said that's how we're gonna to take down the drill. The same way Ty Lee took down all these big earthbenders. Toph chimes in by saying,"By hitting its pressure points!" Aang summarizes what was just said. Toph earthbends a creating an enormous dust cloud for them to use as cover. Toph tells them to stay close. They all run into the cloud. Ty Lee sees the dust cloud through the periscope and says that it's poofy. Azula looks at War Minister Ching and he reassures her that it's nothing.
Everyone is running in the dust and Toph creates a tunnel and tells everyone to get in. Sokka says how it's a dark and Toph sarcastically says,"Oh no, what a nightmare." Sokka apologizes for being so careless. They all come out of the tunnel and are under the drill. Sokka sees an open hatch and Aang helps them all get into the drill. He tells Toph to get on and she explains that she wouldn't be able to see and that she'll help from the outside. Toph wedges a huge rock against the drill and to slow it down. Sokka says that he needs some schematics of the drill and Aang asks where they're going to get it. Sokka swings his machete taking off a wheel to a pipe. Steam starts to rush out of it. At first Aang and Katara don't get why he broke that but Sokka explains and they understand. A firebender engineer walks out of the mist and turns around. Katara freezes all of the steam and the engineer too. Sokka takes a schematic from the engineer and the gang run up some stairs. Sokka examines the schematic and explains that they need to cut through the braces that hold together the inner mechanism and the outer shell. Iroh and Zuko are sitting on a bench. Jet comes over and sits next to Zuko. Jet asks Zuko if he has any plans once in the city. A tea cart comes by and Iroh asks for some Jasmine. Iroh spits it out disgusted and complains that it's cold. Jet asks Zuko if he could talk to him. Zuko heavily sighs. Jet tries to convince Zuko to join the Freedom Fighters but Zuko declined. Jet sees Iroh drinking hot tea and then Jet is sure that he's a firebender. Zuko knocks the tea out of Iroh's hand and scolds Iroh for firebending his tea in public. Iroh says, "I know I'm not supposed to cry over spilled tea, but it's just so sad." Sokka, Katara, and Aang arrive to the braces. Sokka comments on the of the braces. Aang and Katara slowly slice away at the brace. After half way through one brace both Aang and Katara are exhausted. Sokka tries to cheer them on and almost gets water whipped by Katara. They cut through one brace and they are both beat. Aang and Katara both don't know if they can make it in time. Suddenly, there is a loud rumbling and the entire drill shakes. They think that they finished the drill but then War Minister Ching comes over the announcement system and explains that they have made contact with the wall. Sokka is uselessly pushing as hard as he can against the brace Katara and Aang cut through. Katara says that this is bad. Sokka then says how they're putting everything they have into cutting down the braces. Aang then explains that they don't need to cut all the way through the braces just enough and then he'll give the final blow. Aang reminds them that everyone in Ba Sing Se is depending on them. Toph is still slowing down the drill painstakingly. Aang and Katara are still cutting away at the braces. Earthbenders on the wall are throwing tons of boulders at the drill but to no avail. A soldier informs the war minister that the engineer was ambushed, and another tells him that a brace was cut clean through. Azula says, "Let's go ladies." Aang and Katara are still cutting through the braces. Sokka is in the middle of cheering them on when a blue fire ball comes down. He dodges and screams. Ty Lee exclaims, "Wow, Azula you were right it is the Avatar... and friends." Sokka waves and says,"Hey." Katara pulled him away. Ty Lee dove towards Aang and he airbended her away. They split up and Katara gives her water sack to Aang. Mai and Ty Lee follow Katara and Sokka. Azula follows Aang and says that the Avatar is hers. Sokka and Katara come to a hatch that reads: "slurry pipeline". Katara asks what it means and Sokka says that it's their way out. They jump down into the muddy water and get carried away. Ty Lee and Mai look down into the pipe. Ty Lee tries to get Mai to go with her but Mai persistently refuses. Ty Lee shrugs and jumps in. Mai closes the hatch after her. Aang speeds past numerous engineers and control rooms with Momo on his back. He goes up a ladder to deliver the final blow. Katara and Sokka end up outside of the drill covered in wall sludge with Ty Lee close behind. Katara bends the water in the mud creating a plug with Ty Lee in it. Sokka tells her to keep it up so that when Aang delivers the final blow it'll be ready to pop. Aang picks a spot on the top of the drill to deliver the final blow to. Suddenly, several boulders fall from the sky. One of the boulders nearly hits Aang. Aang tries to tell the general to stop shooting rocks and then right after the general says, "Soldiers, whatever you do, don't stop shooting rocks down there!" Aang uses the water to weaken the spot where he is going to deliver the final blow. Katara is still holding back the slurry to build up pressure. Sokka is cheering her on and she finally gets fed up and pushes him down with slurry. Toph asks if they need any help and Katara asks her to help plug up the drain. Toph earthbends the earth causing the pipes to be about to burst. Aang is still working on weakening the spot and stops to say, "What I'd give to be metal bender." Momo shrieks and they turn around to see a blue fire blast shooting towards them. Aang dodges it. Aang sends Momo away for his fight with Azula. Azula shoots several balls of fire at him. Aang dodges them and shoots an airbending blast back. He uses his water whip to knock Azula's blasts off target. She kicks two fierce blasts and Aang tries to block them with water but it evaporates while he is knocked back. Several boulders start falling again and Aang takes the opportunity to shoot one at Azula. She ducks in time and shoots a fire ball. Aang creates a wall of rubble and shoots rocks from the wall at Azula. She kicks them away and almost gets Aang's head with a kick of flames. Azula somersaults in the air and does a really powerful fire blast destroying his wall. Aang hurtled into the wall and falls unconscious on to the ground. The drill extends again and Azula walks over to Aang to deliver the final blow. Azula picks Aang up and holds him against the wall. She forms a blue flame in her hand while Aang is coming to. He quickly makes an earth glove and blocks her attack which knocks her several feet back. Slurry spews from the wall which causes them to lose their balance and crash into each other. They both begin sliding off the drill. Azula is able to stop herself and Momo helps Aang back on his feet. Aang thanks Momo and runs to the weakened spot. A rock falls right next to him. Aang shapes it into a nail and goes high up on the wall on an air scooter. He races down the wall and successfully gives the final blow just missing getting hit by a fire ball by Azula.
Toph makes an island blocking them from the flood of slurry. Iroh and Zuko are on a train with Hope's family heading into Ba Sing Se. And Zuko still wants to go after the avatar. Sokka still tries to give the team a name but gets no one's approval.