Zhan's carriage brought them to the edge of the lower ring and past it far out of Omashu to a small gorge flooded with rainwater.

Sato received them at the lip of it with five other earth benders dressed in full green and black Fire-resistant armour with water pouches fitted to the chest and back of the bust. Aaron assumed the water was for protection in case they were set on fire despite the armour.

Zhan bid them all farewell before he departed.

Mark whistled as he walked up to one of the guards. "Fancy armour, but it doesn't look particularly comfortable."

"That's because it's designed to keep you alive," Aaron said. "It looks like Jade Guard Armor."

The measurements and plate proportions were off, but the armour looked like it'd been modelled after the drawings Aaron had seen of the Jade Guard during his studies.

"You're familiar with the Jade Guard?" Sato asked as he approached them.

"They were my favourite Earth Nation troupes growing up," Aaron said in a dreamy voice. "Trained from the moment they could walk; the records say they had the skill of 10 men and were terrors on the battlefield."

Sato nodded with approval. "They were legendary, and their armour is the closest thing a soldier could get to full fire resistance. We'll need it if we're facing the type of man that melts those who disappoint him."

He snapped his fingers, and two of his men stepped forward with crates in their hands.

"Suit up," Sato said. "He probably knows we're coming."

It took nearly an hour to fully strap on their armour, and Mark threw questions at Sato the entire time. He asked his most important question as they came to the back of the gorge to the only bit of dry land.

"What happened to the Jade guard?"

Satob broke his stride when he heard the question, and Aaron passed Mark a look.

"You talk about them in the past tense. It's not that hard to put two-and-two together?"

"The Dragon of the West happened," Sato's stoic face turned dark. "He knew he would lose too many men in a straight-on fight, so he laid a trap and cornered them with hundreds of firebenders who cooked them alive in their own armour. All twenty of them died."

Mark looked down at his armour with a frown. "Well, that certainly doesn't inspire confidence in their knock-offs. And that's far less honour I expected from the great General Iroh."

"The battlefield is no place for honour," Aaron said, and Sato nodded.

"The winning side writes the history, young bender," Sato said. "Never forget that,"

Mark muttered something under his breath about disrespecting him because of his size. Aaron ignored him.

Sato gestured at his team with hand signs as they came to the back of the gorge. All five men took a horse stance, raised their hands as one and pulled down. A large section of the wall came down, revealing a tunnel that led down into shadows, dimly illuminated by green crystal light.

Aaron's eyes went wide as several things clicked into place. Omashu loomed in the distance, separated by a massive pit carved out of the surroundings. Judging from the angle of the tunnel's entrance, Aaron guessed that the tunnel probably sank deep enough to sweep underneath the bottom of the pit separating the mainland from the city.

"You have a network of tunnels leading in and out of the city," he said.

Sato smiled. "Only a few actually reach the city. The tunnels below are more of a trap than an escape route. Only someone with maps to the under city has any hope of making their way through. There are pitfalls, traps, and creatures that lurk in the dark."

"Then why does Vulcan think it's a smart idea to pitch his tent in a death labyrinth?" Mark said, squinting into the dark. "Is it possible he has a map?"

Sato frowned. "Only the noble houses and the Royal family have maps to the Undercity, and everyone's map is accounted for."

"So, we are either facing a psychopath, or you have a traitor from the noble line," Mark said. "I don't know which is worse."

"I suppose we'll have to ask him before we kill him," Aaron said as he stepped into the tunnel. The rest of them marched in second after.

—

Sato led them through a series of winding tunnels, guided by a map etched on moleskin. They had to double back several times, avoid pitfalls, and Mark stepped on a tile that triggered a trap that shot poisoned bolts at him. If not for Aaron pulling him back and Sato earth bending a chunk of gemmanite at the bolt, Mark might've died.

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It would be hilariously tragic, given it was Aaron's first day of forced protection. He still didn't know how he felt about that. From discovering he was an uncle to being removed from the Avatar's team, everything felt new and raw.

"Jesus, this place is the stuff of nightmares," Mark grumbled, and Aaron felt that much clearer on his position about the boy. Rescuing Mark might be the worse thing that'd ever happened to him.

"How far are we from Vulcan?" Aaron asked.

"Not far," Sato muttered.

When Aaron pressed the matter, Sato showed him the map. It was ancient enough that sections of it had faded, and Aaron wondered out loud how old the Undercity was.

"The beginnings of it were etched into Omashu's hillside before the first brick of the city was pulled from the pit surrounding the city. And every King before King Bumi's grandfather added sections to it. You could spend months exploring the labyrinth below, and it's said that some of the rarest gemmanites in the world were mined from here before the war."

"Sounds like a dungeon to me," Mark muttered, then shivered. "You're going to give my System ideas."

Aaron almost chuckled.

Laughing at Mark's misery would certainly be a highlight of the new job.

It brought a much-needed levity that had him thinking about the fight ahead. Vulcan was more of a threat than Zhan was ready to admit, and Aaron didn't fancy their chance against him in the tunnel with limited breathable air deep underground.

Luckily, they could seal him off and work around him and his men if it came to it or collapse a section of the tunnel down on them. There were many ways to deal with a temperamental Firebender without fighting him.

Sato found Vulcan's hideout sometime after his fifth, "Not far." By now, Aaron was sure they were somewhere under the city. And it also partially solved the mystery of how he continued to operate even after King Bumi removed his inside man. Vulcan probably had a path into the city and at least a few earth benders with him.

But Sato disagreed. "It's unlikely. Every person we've captured said his inner circle members were firebenders and martial artists. We have facilities spread out miles below the surface and trained soldiers patrolling them. He's not getting past them. There's also the matter of the underwater reservoirs below the city."

"We are still clearly missing something," Aaron argued, and Sato grunted.

"Uma, I need you to scout ahead," Sato said to one of the five men he'd brought along. He was short and portly, with a thick beard and bright green eyes.

He saluted the captain, opened a hole in the ground with a stomp, and disappeared into it.

"I'll follow him."

"Follow him how?" Sato asked.

"With his loopy Chi-bending magic," Mark chimed in. "He sits down and becomes clairvoyant or something. I don't understand it much myself."

Aaron tuned both of them out as he settled into a meditative pose on the floor and connected with the ambient Chi with his One-With-The-World as sparse as it was, but it allowed him to follow Uma easily enough.

He moved fairly quickly underground, like a fish, and Aaron wondered if the technique was some proto-form of advanced chi manipulation.

Uma came to masses of Chi behind a bend a fair distance from the group, and he settled in the wall in the far corner, watching them.

Aaron tried to focus on each signature he found, but most blended into a bright mess of colours, except for one. He glowed like a bonfire, yet he had an earthy darkness to his aura that Aaron typically perceived from Earth benders. Aaron fixated on it for the longest while before he gave up, chalking up the abnormality to a mixed parentage.

Uma eventually returned, but with a notable frown on his face.

"They're looking for another way into the city," he said. "There was a freshly dug tunnel inside the chamber they were holed up. I counted over twenty of them."

"They're a bit more than I anticipated, and it seems he has earth benders too," Sato said, "but we press on regardless. The Earth is our advantage, and we will use it. And as for Vulcan, Aaron will handle him."

Aaron saw the tension in Sato's body, some of which he shared himself, but when all eyes turned to him, he showed none of it. He gave a short but confident nod.

Uma expanded on hideout layouts, pointing to guard positions, their cargo bay, and their personal quarters. Sato laid out the plan of attack, suggesting a mode of attack Aaron hadn't even thought possible.

"Take your places," Sato ordered, and his soldiers dove into the walls with a deep rumble, kicking up dust.

"We will flank them," he said as he led Aaron and Mark toward Vulcan's hideout. "We are distractions, and the team is the hammer. When the fighting breaks out, you will run to Vulcan," he said to Aaron.

"What about me?" Mark asked.

"I'll be playing protector while Aaron is busy. The King said I should allow you to test yourself without endangering your life."

"That's oddly thoughtful of him," Mark said, and Aaron huffed.

"He gets to be someone else's headache for a change."

Mark shot him a furious look, but the latter rolled his eyes.

Aaron heard the smuggler's bickering voices before he ever saw them.