The first thing Toph noticed was the noise.
As they approached on Appa, her seismic sense was unable to help her, but she heard several incredibly loud objects rumbling from a direction she presumed to be beyond the walls. It was only after Appa touched down and she got her feet back on solid ground that she knew the scale of their problems.
She had encountered the type of giant drill that now rumbled inexorably towards them before, when they had first arrived in Ba Sing Se and had stopped the Princess Azula from using it to bore a hole through the walls. That time, there had been one of them.
Now, there were three.
Just along the wall from where Appa had landed, one of the Generals on the Council of Five, Toph couldn't remember his name, was speaking to his subordinates.
"..last time, the Fire Nation attacked with one drill, with barely any support, and we still barely stopped them. Unfortunately, it seems that whatever else can be said about Ozai, he learns from his mistakes. Three drills, with substantial backup from infantry and tanks."
"We can do what we did with the last drill!" Sang volunteered. "The only problem is we'll only be able to stop one of them."
"The general sighed. "It's the best plan we have."
"Aang!" Katara, Sokka and Suki all talked over each other at once. "You can't seriously expect this to work!"
"I don't. It's the best plan we have though."
And with that, Aang jumped off the wall and flew towards the nearest drill on his glider.
"So I guess we improvise," Sokka grumbled.
"Again."
Appa touched down on top of the first drill, and Toph jumped down, followed by Katara, Sokka, and Suki, a second later, Aang was beside them too.
"The best plan I can come up with at this moment is just to get inside and somehow destroy the engine," Aang said. "Maybe if we waterbend the steam in the pipes?"
"It's worth a try."
Sneaking into the drill was a lot harder than the last time, partly because they had approached from above where everyone could see them and partly because the Fire Nation had learned from their mistakes; the place was crawling with guards. Most of them were dealt with easily, finding themselves with a faceful of steam, a boomerang or a sword to the back of the head, or being suddenly propelled forward head-first into a wall.
Soon enough, they were in the engine room. Katara and Aang closed their eyes, and concentrated. With a movement of their arms, the place rumbled as pipes across the entire drill ruptured. However, just as it seemed the engine might be stopped-
"Guys, we've got company!" Sokka shouted. Toph could hear the clatter of boots on the metal floor coming towards them.
"We'll hold them off!" Suki added, as she and Sokka went to guard the doorway. Toph heard shouts, before the sound of a full-blown fight came from the corridor- including the tell-tale swoosh of firebending. Suki was good, and Sokka was getting there, but against Firebenders? Toph didn't like those odds, and so resolved to go after them. Leaving Aang and Katara to their steambending, Toph ran out after them. She found the two fighting back to back, Suki with a fan in each hand and Sokka with his boomerang in one hand and his club in the other. Already a small heap of unconscious Firebenders lay at their feet, rather more on Suki's side. "Toph!" Sokka called, seeing her. "Look out!"
Toph didn't need to turn around to "see" the Firebender lunge at her, and was able to duck under his lunge. She heard the crunch as he ran straight into Sokka's club. She herself was powerless here; the only Earth was far below her, separated from her by several layers of solid metal.
Just then, the flow of Fire Nation troops in the corridor finally became too much for Sokka and Suki to hold back, and the two were forced to retreat, with Sokka grabbing Toph's hand to pull her along with them.
"What about Katara and Aang?"
One is a Waterbending master in a room surrounded by steam and the other is the Avatar. They'll be fine!" Sokka grunted back.
"Oh no," Suki sounded resigned. They had reached a dead end.
The two pushed Toph behind them and turned, preparing to face the Firebenders. Toph resented this, for she wanted to face them alongside her friends and she certainly resented the implication that she needed saving, but they certainly appeared heroic, standing against so many alone.
Wait, Toph realised, how can I see them?
She was surrounded by metal. She hadn't thought that she could use her seismic sense on metal, but come to think of it she had been doing it ever since they had entered the drill. This gave her an idea. Turning her back on the Fire Nation troops, she drove her fists into the wall behind her and concentrated. For a while, nothing happened, but she soon began to make out small imperfections within the metal; imperfections that looked a lot like earth. This encouraged Toph, and she increased her effort, pushing on the wall, willing the earth embedded within to just budge- and it did. Toph stepped back, admiring her handiwork, as all assembled looked at the enormous dent she had put in the wall.
"Toph?" Sokka asked wonderingly. "What did you do?"
Toph turned to face them with a smile. "I just metalbent. And you dunderheads are in a world of trouble."
With that, she stamped on the floor, and the corridor distorted, the previously perfectly straight lines crumpling. The roof came down with incredible speed, crashing into the heads of all the fire nation troops present and sending them sprawling. Sokka, Suki and Toph ran past them, making their way back to the engine room.
They found Aang and Katara still trying to burst the pipes, but now they were surrounded by several fire nation ice statues that had not been there when Toph had left. "Sorry about that", Sokka apologised. "We were overwhelmed."
"How did you fight them off then?" Katara asked.
"We didn't. Toph did."
"I metalbent."
Aang and Katara stared slack jawed at her for a second. "Metalbent?" Aang said after a while. "But that's not possible is it?"
"Aang, by now you should know that I am Toph Beifong, the Greatest Earthbender in the world. Nothing is impossible for me. Watch this."
She placed her hand on the wall and pulled. Sure enough, the wall came with her hand.
"Right, new plan!" Sokka shouted, startling everyone. "We go down to the bottom of this thing and Toph pulls the wheels off." They ran out of the engine room, and made their way to the bottom of the craft. Toph again drove her hands into the wall and concentrated. She felt the inexorable drive of the caterpillar tracks, and willed them away. A loud crash sounded, and the floor dropped away from them. Toph could no longer feel the wheels that had been closest to her.
They then made their escape through the bottom of the drill, and once Toph had her feet back on actual earth she saw that she had ripped one of the tracks clean off; it probably could be fixed, but that drill would not be moving for a while.
They had bigger problems though. The two other drills were getting dangerously close to the wall, and fire nation troops on the ground were beginning to notice them. Aang blew his sky-bison whistle and Appa landed beside them. They all scrambled on and soon were airborne.
"What will we do about the other drills?"
It was Aang's turn to shout in excitement. "Toph can control metal now, so could she crash one of them into the other?"
"I could!" Toph replied enthusiastically.
Sokka muttered under his breath about being the ideas guy, but nobody paid him any attention. Appa hovered next to the wheels of the second drill, close enough that Toph could reach out and touch it. Toph pressed her hands against the machine and willed the metal to bend to her will. With a crunch, the suspension of the drill did so.
"It's turning!" Katara yelled.
"Can we land?" Toph asked. "It's just I can't use my seismic sense up here and I think I'm going to want to see this bit."
Aang duly put Appa down, making sure to put enough distance between them and the fire nation army first so that they could not be bothered, and Toph prepared to "watch." The first thing she heard were shouts, presumably from the crew of the first drill trying desperately to turn and the crew of the second drill realizing what was about to happen. Then came the smash. Using her seismic sense, Toph was able to see the drill of the first machine tear a gash in the side of the second, exposing its internals. At the same time, the metal shards that the drill ripped off became clogged in its system. After a few seconds of the most painful sounds coming from the two machines, they stopped. Without a way of penetrating the walls, the Fire Nation had lost.
One drill had lost a wheel, one had had its suspension completely bent out of shape and its drill mechanism destroyed, and the last had an enormous hole in it. There were now four enormous metal ruins in front of the walls of Ba Sing Se.
"Time to get out of here". The Fire Nation had seen them and the first tanks were approaching. Soon they were all on Appa and on their way back to the wall. "Does this mean I saved the city again?" Toph asked.
"Yes, it does." Aang said. "But don't let it go to your head!"
"When have you ever known me to boast, Twinkletoes?"
"Well..."
"Don't answer that, actually."
With their work for the day done, Team Avatar flew back over the walls of Ba Sing Se.