A/N: It is not clear exactly when the inventor put those rotten eggs into the room with the gas. I'm assuming he did it between when the Fire Nation guy was driven away and when he showed up and offered to help, just because that's the only free time he had. I have no idea when Sokka is supposed to have thought of adding a lid to the war balloon, or when the inventor found the time to install it. Everything in canon seems to happen so quickly, I have no idea where they found the time. Seriously - it was 4 o'candle when they were on their tour, and after the battle lighting conditions suggest sunset is just beginning. In a temple close to the North Pole, in the middle of winter. There's no indication that a night passed in between; all this seems to have happened in a single day. I'm impressed the Fire Nation managed to mobilize so quickly, too. Honestly it would have made more temporal sense if the episode's events had been split across two days, but I understand that would have been less dramatic. Also, it's already been established that the animators weren't paying attention to how day/night cycles work at different latitudes. 4 o'clock is post-sunset in the middle of winter where I live, and that's nowhere near the North Pole. But there might have been a lot of time between 4 o'candle and sunset for all I know.

The part of the war balloon that people stand in will be called the boat because, well, that's clearly what it is. In this world, hot air balloons have circular basket-shaped baskets. In the Avatar universe, war balloons have boat-shaped boats that are literally just repurposed boat hulls. That's just how it is.

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Aang held his staff up in the air. The assembled crowd quieted. "Everyone, listen!" he called. "The Fire Nation is coming. We're going to be under attack soon. But we have a plan to fight back! We have something the Fire Nation doesn't have: air power. With our inventions and our ability to control the skies, we can fight them off."

Katara stepped up. "Don't panic. Anyone who can't fight will be safe in the temple's underground rooms. Anyone who can, get your glider. We'll need it."

Sokka and the inventor stepped forward. "What she said," Sokka said. "Get your glider ready, then come up to the top room of the first tower. We'll present the battle strategy there, along with some new inventions that'll knock the socks off those firebending jerks."

"Children too young to fly have to shelter, along with their caretakers," the inventor said. "This place was meant to be a safe haven, our new home. Please, don't throw yourselves into harm's way. With the Avatar's help, we will repel the invasion. Trust us and keep yourselves safe."

On that note, the mobilization began. The air walkers were greatly alarmed, but showed no signs of panic. The crowd had no difficulty parting to let the youngest children through, along with their mothers and sometimes their older siblings. Aang let out a sigh of relief. He flew to the back of the crowd, where he saw Zuko and Iroh listening. He asked, "Will you help us?"

Iroh nodded. "I will go into the shelters. I understand the importance of morale very well. I can help prevent panic."

Aang looked at Zuko. He had a sad feeling that he already knew the answer, but he had to ask. "You?"

He expected that Zuko would go with his uncle. They would be out of the way there, away from all possible accusations of treachery. Instead, Zuko said, "I'll listen to your battle plan."

Aang and Iroh stared at him. He crossed his arms. "I'm not going to stay underground where I can't hear or see what's going on. If my people are going to fight, I want to be there."

Iroh put a hand on his shoulder. "I understand. Stay out of danger, Nephew, and don't get spotted." He left, following the children into shelter.

"I thought -" Aang started to mutter. But then he thought better of it. Now really was not the time to provoke conflict.

"That I don't have any people?"

Aang gulped. "Yeah. I mean, that's what you said."

Zuko shoved him aside. "Nothing that I said up there matters, okay? Pretend it didn't happen." He joined a group of young men waiting for the children to reach safety first before they went up to the inventor's room.

Aang was more confused than ever. What was going on? What was the truth? When Zuko talked about his people, who was he referring to? It had to be the soldiers, right? Was he going to try to sabotage the plan? No, not possible. He might be angry a lot of the time, but he wasn't the sort of guy who would sacrifice children. Was he?

There wasn't any time to spend agonizing over it. Whatever happened would happen. Aang decided that, once more, he just had to trust Zuko. He had to do what he needed to do and let the firebender do what he would do, and hope there was no conflict between their needs. Aang's palms grew sweaty at the thought. He had never had to trust Zuko in the middle of a battle with the Fire Nation. Which side would the firebender fight on? The whole situation was slippery and unpredictable because he was there.

A memory flashed before Aang's eyes. Zuko looking away, his breathing faltering. He was in pain. No matter what he said, Aang had seen it with his own eyes and knew it to be true. They were alike. Because of that, Aang would trust him with the fate of the fight against the invaders. Aang spread his glider and took off, soaring upwards to the inventor's room at the top of the first tower. He did not look back.

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Sokka frowned. What was he doing here? Zuko leaned against the side of the room, watching their presentation. Was he spying? He might just try to sabotage something to give the Fire Nation the upper hand!

Aang caught his attention with a quick blast of air. He shook his head and smiled, giving Sokka a thumbs up. What? They were going to trust the fanatically loyal prince of the enemy nation? But Katara shot him a stern look, too. Sokka rolled his eyes. He was outvoted. If this decision completely backfired and their wonderful plan went down in flames, nobody would be able to blame him.

The presentation went ahead as planned. The inventor, completely unaware of any possible problem, told the room, "We finally got the war balloon working, thanks to Sokka. This boy's a genius!"

Sokka modestly tried not to blush. "Thank you. You're a genius!"

The inventor modestly turned away. "Thank you!"

Sokka picked up the model war balloon and began to explain how it worked. It took no effort to smile as he did so. The balloon's success was his, all his, and he had every right to feel proud of it. It felt even better to explain his achievement to others. He'd always said he was not a buffoon. Now, here, he truly felt it. He was a genius! Leaving the South Pole was the best decision he'd ever made. Invention could be his thing!

Then he and the inventor took turns explaining the main strategy. The gliders would be equipped with bombs of four different types. From above, in a series of strafing runs, they would bomb the Fire Nation soldiers as they marched up the narrow and snowy pass that was the best way up the mountain. The soldiers wouldn't be able to fight back, not from that precarious position. As long as the supply of bombs held out, they would not be able to advance up the cliff. "Then comes the war balloon. The war balloon will be loaded with extra-large slime bombs. We'll find their main force and trap them all in slime. That will force the soldiers to retreat. Any questions?"

There were none. Sokka glanced over at the firebender/possible spy. He seemed really tense all of a sudden. Sokka turned to Katara to ask her to use her deductive skills to figure out why. Katara, however, was too busy telling the inventor that she and Appa could serve as an aerial reloading station. The inventor approved this plan, then waved for Sokka to follow him. "Come on, boy! We're going to have to hurry if we want to have the war balloon ready in time. I've got to finish installing the lid, then we have to load it, then get it ready for launch. Hurry!"

"Wait." Zuko came up. "Take me up with you."

"Why?" Sokka asked.

"Thank you! We'll need all the help we can get." The inventor clapped him on the back. "Sokka, get the bombs ready. This boy and I will prepare the balloon." He hurried out of the room. Zuko followed.

Sokka let out a high-pitched cry of frustration. "I can't be blamed for this, I can't be blamed for this," he repeated. "If he burns down the whole balloon and this place gets overrun by soldiers and the people have to run for their lives and maybe get caught in the snow and quite possibly freeze to death, nobody is going to blame me." He held his strong posture for a couple seconds, then wilted. "Except for me."

He ran to gather all the bombs that had been prepared so far, and ran to deliver them. As he ran, he hoped and prayed that disaster was not breaking out already deep in the bowels of the temple.

.

"Wrench!"

Zuko grabbed the wrench and threw it up to the inventor, who only had eyes for his balloon.

"Nuts!"

Zuko leaped up to hand him nuts. The inventor took them without even looking and started to attach the lid. "Those ropes over there - tie them around the boat. Tightly; they'll be carrying a heavy load."

Zuko hauled the thick ropes over and tied one end of each of them to various places on the hull of the boat. Did this count as helping? He rationalized that no, it did not, because Sokka and the inventor would have tied them on anyway. It just might have taken them a little bit longer.

"What's your name?" the inventor asked.

"How is that important right now?"

"Well, I need something to call you."

Zuko did not want his real name being called out in hearing range of the Fire Nation, but he hadn't thought of a fake name. Uh oh. What do I say? "If you ask the kids here, I'm a dragon," he said, stalling for time.

"Good," the inventor said. "Dragon Boy, hand me that can of oil. This lid was an old piece of scrap. It needs oiling."

Zuko handed him the oil. He had mixed feelings about his new nickname.

A loud scraping noise mixed with the sound of groaning came from the hall outside. Several seconds later, Sokka staggered into the doorway on the edge of collapse and too out of breath to speak. He managed to smile at the sight of the intact balloon and vaguely wave at the barrels of slime he had dragged in before collapsing.

"Sokka!" The inventor climbed down. He pointed off to one side. "Underneath that contraption are several sheets of spare canvas. They'll do as bomb wrapping. Pull them out and start filling them." He ran to Sokka. "Sokka, don't exhaust yourself. I know we are in a hurry, but you'll be no use to anyone if you're too tired to fight."

Zuko dumped a barrel of slime in the center of each piece of canvas, after determining that it was sludgy enough not to spill. The inventor propped Sokka up against a wall and helped gather the canvas up and tie it. He lifted the bombs himself to measure their weight. "Agh! These things are heavy. I think three people plus these is the limit of what this balloon can carry without losing altitude. It's a good thing we don't need to fly up."

"Maybe we'd have an easier time launching this thing," Sokka wheezed, "if we only had two people."

"No!" Zuko snapped. "I…I have to see the battle. I can't stand by not knowing what's going on. And there's no extra glider for me."

"You've been a great help," the inventor told him. "I am confident in the strength of my invention. It'll be fine."

Sokka got to his feet and stumbled over to discuss their strategy and perform final checks on the balloon. Zuko turned away. He clenched his fists and pressed them against his head. This is exactly the situation that Uncle warned me about! I need a plan! Come on, come on, come on. What am I going to do? His brain threw up nothing but blanks. The harder he tried to imagine actions he might take, the clearer his mental image of a blank cream-colored white wall became. The only thing he knew was that he had to see the battle. Beyond that, he had not the slightest clue what he was going to do. He gritted his teeth. I should help someone. I should do something. But he could not imagine anything to do, let alone make a decision. He did not have a plan, and no plan was coming, so he was all adrift on the river of time: a victim to whatever happened. No! I can't be impulsive again! I need to think rationally. Come on, come on. But his capacity for rational thinking and planning had evaporated just when he needed it most.

"Tie 3 needs retying," Sokka said in a rush while retying it.

"The rudder needs oiling," the inventor said while oiling it.

Sokka leaped into the boat. "Now we need to get it ready for launch."

The inventor shooed him out. "I installed a secret back door to this room when I built the balloon. I thought I might get a chance to perform test runs on the real thing before they arrived to pick it up. It's over there. Clear out the junk and open it while I fuel the balloon. We'll have to perform a direct launch."

Zuko and Sokka tossed other inventions aside, not caring if they were damaged in the process. They uncovered the door and located a lever. They both grabbed the lever and pulled down on it with all their strength. The door rotated on a hinge, opening up to the cold mountain air. The sounds of explosions could be heard, and worse: clanking metal. A shiver ran up Zuko's back. He had known the Fire Nation army had more than foot soldiers at their disposal. I can't believe they actually brought them. Tanks? Against an isolated temple full of peaceful people? Why?!

Sokka leaned as far out the door as he dared to take a look. "I can't see much, but it does not sound good out there. What are those things?"

"Tanks," Zuko said. "They're impervious to everything except a precise hit through the fire-slots."

"You're kidding me," Sokka whispered. Horror filled his voice. For once, Zuko understood exactly how he felt. The plan hadn't accounted for anything more than foot soldiers. Even with the war balloon, it was on the verge of failing. Then what would happen to the children sheltering underground, who trusted them as the inventor and Katara had said to do? Zuko found himself thinking of ways they could defeat the tanks. What? No, those are my people. But Iroh was down in the shelters too. Zuko despaired. I just don't understand! How could they? These are peaceful people. Why attack? Why?

"Activating the burner now," the inventor called. "Sokka, Dragon Boy. Load the bombs in the boat. We'll deploy them once we're airborne."

"Dragon Boy?" Sokka asked while lifting a bomb.

Zuko didn't respond. He couldn't. His throat was too tight. I don't understand. This doesn't make any sense.

After several slow, agonizing minutes with the burner on its highest setting, the balloon filled with hot air. The boat lifted off the ground. It was only by an inch or two, but that was enough. They pushed it in the direction of the door and leaped in just before it entered open air. Sokka grabbed the rudder and steered it in the direction of battle while Zuko and the inventor deployed the bombs over the side.

Zuko staggered to the side and tried not to fall overboard. The scene outside was straight out of his worst nightmares. Tanks and soldiers marched toward the base of the temple, with more following. A few gliders remained in the air, but most were landed on the takeoff area. Appa was there too - even the Avatar couldn't stop this. The sight of the Avatar and his friends not even trying to fight off the tanks filled Zuko with despair in a way that nothing else could. He found himself wishing that they would do something, anything. Doesn't he have an Avatar State that can blow the tanks away? Why doesn't he use it?!

Zuko had never been a soldier. He'd never actually seen the fighting at the front lines. He had never imagined it to look like this. From above, the Fire Nation forces looked overwhelming, like an army of ants overtaking and stripping an ostrich horse while the animal screamed and screamed, helpless to do anything about it. Wasn't the Earth Kingdom supposed to be hard and stubborn? Zuko could just see people with their gliders, crying. It's not supposed to be like this.

"Why aren't they shooting at us?" Sokka asked.

"The insignia!" The inventor looked up. "They think we're on their side!"

Sokka wasn't filled with despair yet, somehow. "Then they're in for a big surprise." He cut a rope. A bomb full of slime fell, covering a grand total of two tanks in sludgy but harmless goo. Zuko's stomach threatened to crash through the bottom of the boat and fall overboard without him. It's not enough. It's not even close. We were so stupid to think it could be.

All the bombs were released, and it barely had an impact. "Oh no," Sokka said. "That was the last one."

Zuko closed his eyes. Please, somebody, somehow. Please end this. Please.

Then, the inventor started to sniff the air. "Do you smell that?"

Sokka sniffed the air. "Rotten eggs! There. That's where the gas is escaping!"

Zuko opened his eyes. Gas? What gas? More tanks were pulling themselves up the mountainside even now. All hope was lost. The temple was going to be overrun. And he had stupidly insisted on watching it happen.

Metal creaked as the burner shifted back and forth. "What are you doing?" the inventor asked. "That's our fuel source!" Zuko turned to see Sokka prying it up.

"I know, but it's the only bomb we've got," he said.

Zuko's eyes widened. Explosive gas. That was what they were talking about. He looked down where Sokka had been pointing. They're going to blow up the whole mountain?

Sokka and the inventor tossed the burner over the edge. Zuko could feel it still burning on the way down. It fell into a crevasse, clanging and bouncing off the sides. It disappeared from view. And then…

Whump. The pressure wave hit first, tossing the balloon aside. Zuko clung to the side and turned his head away. The sound, the heat and the dust came later. It sounded like the world was ending. All he could do was hold on to the boat and hope to survive.

Eventually, he heard the sounds of…cheering? Zuko raised his head and looked over the side. His jaw dropped. The mountain is half gone! There was no longer any mountainside for the tanks to climb up. The air walkers had better be happy with their new home, because the path was gone. Blasted, unclimbable jags of rock stuck out everywhere, overhanging a formerly underground cavern. Zuko glanced up at the temple. It was not impossible that with years of weathering and a few unwise construction projects, the temple could become heavy enough to slide down the broken mountain. At least, it looked that way.

And they were cheering. At that moment, having seen what he had just seen, it was too much for Zuko to handle. How could they be cheering for such destruction? The mountain was destroyed! The Fire Nation had been like an unstoppable army of ants, and then the mountain was half gone, and… How could anyone be cheering? He stood up and pushed himself away from the side, swaying. How many people died just now? Then, out of nowhere: Is this what I did when I used the water spirit?

He jumped when the temple started to rise. How could it be rising?! No, it's not rising. We're falling. Zuko looked up at the balloon. It and its giant bombs had started all this. They'd blown up half the mountain from this balloon, and barely taken a risk. That seemed deeply, deeply wrong. It shouldn't be possible. Things like this shouldn't be able to happen.

Sokka and the inventor lost their balance and grabbed at the side of the boat. "We're - rising?"

"Turn this thing around."

Sokka and the inventor turned and saw Zuko standing where the burner had been, a large fireball in his hand. He held it quite steady, considering that the rest of him was shaking. "I said, turn this thing around. Now." The look on his face… It was clear that he would not be hearing any argument on this matter. Sokka went to the rudder and obliged.

"You're a firebender?" the inventor asked. His monocle threatened to fall off.

Zuko nodded. He really didn't care what the man knew. He didn't care about anything anymore. Only one thing mattered: This should not be allowed to happen.

The inventor closed his mouth and picked up the rope controlling the lid. Without the weight of the bombs, they had inadvertently risen high into the air. With Sokka's experienced rudder control and the inventor's careful lid manipulation, they managed to bring the boat down on the landing area with only a minor jolt. Zuko extinguished his fireball when they were still several feet above the heads of the crowd. The inventor left the lid open, allowing the balloon to deflate while they climbed out.

Another great cheer went up from the crowd. People ran up from all sides and embraced Sokka, clapped the inventor on the back, and generally made a great big fuss about them. Nobody noticed Zuko taking a step backward and slipping a candle flame onto the side of the boat. He walked forward and got himself involved in the fuss, then told the fire spirit to let loose.

Flomm. The cheering ended in a burst of shrieking as everyone jumped away from the enormous flames suddenly engulfing the whole balloon. The heat was intense enough to scorch the back of Zuko's neck. He retreated to a safe distance. Everyone there watched the balloon burn in silence. It didn't take long. Even the metal parts did not survive.

The inventor and Sokka looked sideways at Zuko. He touched the back of his neck and winced. The pain helped bring clarity back to his senses. The terror and wrongness he had been drowning in receded. There. Now nothing like this will ever, ever be able to happen again. The relief left him exhausted. He struggled not to collapse like the balloon without its burner. I knew this was the worst day of my life.

"Nephew? Are you alright?"

No, but I did my best. Zuko's vision swam. He closed his eyes and passed out, straight into his uncle's arms.