[Three days later]

A dreadful scream resounded in the yard. Zuko leapt up, finding himself a fraction slower than Suki who was already leading them, and the four raced outside. Piandao had also heard, and he and a pair of students came from the staircase and merged with their group. They had not far to go, as the cause of the woman's distress was immediately apparent.

"Appa!"

Nuwa was on the ground in a terrible state of alarm. "A monster. Master, a monster, save me!"

Aang leapt down from the saddle and began profusely bowing to her in apology. "He isn't a monster, he's a flying bison. Appa is a vegetarian, don't worry, he won't hurt you. I'm sorry for scaring you." Mid-bow he looked up and saw them approaching. "We got your letter, Sokka."

As to 'we', a small figure in green slid down the side of the bison and approached them. "Well, I for one had no idea she was standing there before we landed," she stated casually, and stood without looking at anyone in particular. "This is on you, Twinkle-toes."

Aang helped the older woman to her feet and tried to calm her down while she muttered about the bison dropping from the sky like a demon. Aang apologized to her again, then turned to introduce the girl. "Everyone, this is my earthbending sifu, Toph Beifong." She was about eighteen, slender, and barefoot. Over her shoulder hung a dirty tan daypack, and her eyes were a cloudy pale green. Zuko had heard of their family, one of the wealthiest in the Earth Kingdom.

While the servant scrambled away and retreated into the mansion, everyone introduced themselves. Zuko stumbled back as a weight crash-landed on his shoulder. Momo, enthusiastic, chittered and leaned over to peer into his face, giving him a whiff of lemur-breath, vaguely fruity. He'd known they had Appa at hand, but it surprised him how quickly they had managed the trip, almost like they were eager to be out of Gao Ling at the first chance. After the city had been razed into ash by Zhao and Azula, they'd sent an embassy and engineers to aid them in rebuilding. He'd received an earful from the advisors for how much money he'd set aside for their restructuring; it had been the first and last time Zuko'd had to demonstrate his uncle's fire-breath. Most of the captured earthbenders had been held as prisoners of war, but that wasn't to his advantage, as they had been in an exceedingly poor state of health when released back to Gao Ling, and were surely armed with unpleasant things to say about his country.

Aang continued the introductions, saying, "And this is my firebending sifu, Zuko. He's the Firelord now."

Toph wasn't impressed. "Well, go on, then. Let's have some firebending. Nice and close so I can feel the heat." She swept up her bangs and pulled her eyelid down. "Visuals aren't my thing."

Everyone looked to him. Clearing his throat, he approached and held his hand out with the palm upturned, then produced a flame there. She stood without reaction, then shifted and stomped on the ground. Zuko extinguished his fire and fell to one knee as the ground rose into a pillar under his feet. He was held ten feet in the air on a surface two feet wide. "Mine's better," she said, then grinned as she lowered him back down. Aang was suppressing a laugh, and turned his face away when Zuko glared at him.

The students were introduced as Haoran and Caishen, Piandao's top students besides Sokka. The three had grown close during training, and they were thought trustworthy. Their families had mostly refrained from joining the military in the past. Haoran's oversaw a prosperous farming region and had made themselves a good living through the generations, and had helped in previous times of famine during the reign of Azulon by donating all of their own grain stores and dried provisions to the citizens free of charge. Caishen's family were artisans famed for intricate metalcraft, and had invented new household apparatuses that made life more convenient for Fire nationals. Upper end restaurants started bidding wars over their wares. "If you need any assistance, these two can help you, Avatar. Only Haoran is a firebender, but they're both skilled at swordsmanship and archery."

Leaving the Kyoshi Warriors to figure out what to feed Appa, they went inside to tea, taking the dining hall with a view of the garden, and caught the two arrivals up on what had been happening. Yue, at that time, stepped into the room with her friends and the Kyoshi Warrior pair in tow. Suki dismissed them both to take a break, and the princess and two women took seats. "Avatar Aang, you look well," said Yue with a smile. She seemed wary of the student pair, but otherwise looked to have recovered a better mood. Wen, the girl who had insulted Katara, wore Yue's necklace. She had changed completely from that petulant, hostile girl with a broken nose into a bright demeanor, and, once in a while, happily stroked the necklace like a comfort.

Aang was glowing in newfound confidence, nearly seventeen and more mature. He was boyish on the edges, but his core was strong, like a reed and upright. Wrapped in a new outfit of yellow and orange robes, he was growing more to resemble the monk in saffron. He told them of everything that had occurred since they parted ways at the North Pole and how far he'd progressed with his earthbending. "Things clicked for me about two months in. Now I'm just as good as the military instructors at Ba Sing Se. I can lift a boulder the size of Appa."

Katara commented, "Aang always struggled with earthbending. How did you do it, Toph?"

"I broke him down crying and bloody, and remade him in my image."

Everyone paused. Sokka in particular looked uncomfortable, probably remembering his own breaking-in by Suki. Aang, like an offer for tea and dessert after a fiery meal, said, "We trained a lot and I only cried sometimes. Toph explains things well. To learn anything you just need the right teacher, someone who speaks your language and can phrase things in a way that feels native to you."

"I also hurled rocks at him. That was the fun part."

Nuwa, recovered from her shock, entered with a tray of snacks and set them on the table, then left back towards the kitchen. Her hair was dark brown with gray streaks, and she had a number of age spots around her collar and hands. "Well, Sokka has good news, too," Katara said, and prompted her brother to take over.

He cleared his throat. "Suki and I will be getting married soon. It will have to wait until this trouble is over, but I've received the blessing of her parents and Dad has approved as well."

His sister gave a wry smile. "Go ahead and tell him why you waited so long."

He looked bashful. "I was waiting until I could beat Suki in a fight."

"So, you can take her in fight?" asked Aang dubiously, measuring looks between the pair.

"Well, sometimes," Sokka admitted.

Suki, glowing with pride, said, "All he needed was a good teacher and some time to practice. He's my best student."

"Hopefully you can tackle sock-mending next," teased Katara. Yue looked to Suki, then placed a fingertip on her own bare neck. Katara, changing the subject, said, "Now that we have tea, we should probably get down to business. Aang, something is going on. Yue was attacked here, and then someone drugged me and gave me a creepy letter about strange, awful waterbending techniques I've never heard of before; moves that, if known, would make everyone fear and hate waterbenders. It seems like someone wants to restart the war."

Piandao added, "We've been investigating, as both incidents occurred on campus here, but we haven't found anything conclusive. The culprit must be familiar with the property and have an easy way in and out. Do you have any ideas, Avatar?"

Toph snorted. "Well, that one's easy. They're using the lava tunnels." Everyone looked to her in shock, and she took the silence as a cue to elaborate. "Underground, there are tunnels that formed from lava flows long ago, long and mostly flat or only a slight slope. I had a servant read books out loud to me at home, and I had one about volcanic landmasses, how the earth there formed and what it was composed of. This island was created by volcanic activity. It makes the ground feel weird, like those floaty rocks with all the holes in them."

"Pumice," stated Sokka.

"Yeah, that. I made my father buy me different rocks and crystals from all over the world so I could feel them. Unfortunately they were buried when our house was destroyed in the assault on Gao Ling, but I recovered them from the wreckage when we went back and some of our belongings. It was the first time I ever saw my parents happy that I'm an earthbender."

Piandao laced his fingers under his chin. "Where do these lava flows go?"

"All over the area here, for miles and miles; there's an entire interconnected system underground."

"I've heard about this," said Piandao. "Sometimes people break into one when digging a cellar for a house or a well. Can you guide us to one?"

"Yes, but they're pretty tight. It would be best to only take a small group down."

They settled on Zuko, Aang, Toph, and Sokka. That evening they went into the yard, in an area of plain grass, and waited as Toph walked around, taking long times to think and occasionally stomping, plotting out a diagram in her mind of where they ran. Finally she decided on a spot and led them there. She had them stand back and then, taking a bending stance, she excavated the surface covering and carved a staircase into the side leading down to the chute. "After you," she said.

Zuko went down first. The inside was pitch black as soon as they were out of the sunlight from the opening, so he lit a flame and sent a course down either direction to check if there was anything there. With the coast cleared he called the others down after him. "Which way?"

"This way. It leads towards where Yue was attacked," said Sokka. He followed Zuko in that direction. Aang could light his own flame, and, meanwhile, Toph didn't need one. She was the most well-equipped for that terrain. Only their two handheld fires provided light. "Toph, how far does this go?"

"Pretty far. I can't feel the end. I've heard the longest lava tunnel ever found is forty miles long."

The tunnel was fairly even and rounded into an oval shape, and there were no sudden drops to worry about. If Zuko raised his arm, his hand would touch the ceiling flat. It was unpleasantly claustrophobic, and he was glad only the four of them had gone down. Sounds echoed in a strange way and made it seem like someone else was down there, walking somewhere close by. Sokka was contemplative, walking with even paces like he was counting off their distance. The walls were oddly smooth in most places, like they had been melted, and red minerals gritted across in streaks periodically. When he looked back, he could no longer see the light from the entrance.

The slope tilted downward slightly and they were descending. They must have been off the mansion's campus entirely by then, and had been walking about fifteen minutes. Toph remained adamant that she could not feel the end of the run. Once in a while, Sokka stopped to examine the ground or feel a hand along the wall. Otherwise they walked in silence, wary should they meet anyone else down there, as well as seeking to avoid the dizzying echo.

Behind him, the second flame wavered and began flickering madly. Zuko turned back. "Aang, focus," he whispered.

"Sorry. It's just, I'm not sure if I heard something."

They paused. Toph slid her foot around on the ground pensively, feeling for the vibrations, and they waited without moving a hair for her to finish her assessment. "There's nothing moving out of the ordinary. Some insects and animals, some water."

"Water?" asked Sokka.

"The water table," she whispered. "It seems like the ground is solid, but about ten feet below us pockets of water are beginning to form. They join up even deeper and form a reservoir. It's what wells tap into. The water trickles down from the surface, filtering through the earth, the sand and rocks and soil. Like little rivers underground."

They continued walking with a new appreciation for their surroundings. If not for Toph they would never have discovered this, and, if the tunnels were being used by the attackers, they would have remained unknown. However, one thing continued to bother Zuko: where they were surfacing. There were no exposed openings within the boundaries of the mansion's property. When he looked back he could see the rise in the ground extending into blackness. They were still gradually descending, and he didn't know how far it would continue, or what lied above them by that point. Toph's face was tight, and her bravado was cooled into wary concentration.

Sokka stopped them, and crouched to look at something on the floor. "Ashes from a small fire, maybe a torch. There's only a faint trace." He smoothed his finger over the spot, raised his hand to his eye level, and rubbed his fingers together. "Someone was here. Let's keep going."

Zuko found it disturbing, but tried not to show it. He was out of place there. In a confined space, fire could consume all the oxygen available and leave the air heavy and flat, making it increasingly difficult to breathe, and that thought plagued his mind. He desperately wanted the young woman to open a ventilation shaft but knew they could not risk it. They walked another ten minutes. Sokka kept his eyes sharp but uncovered nothing further, and no one spoke, under a certain pressure from the verification that they might not be alone. He wondered if they would go all the way off the island, to below the ocean floor, and imagined the enormous pressure above them from the weight of the earth and sea pressing down. However, if there had been someone else passing through the tunnel, it must lead somewhere eventually, and that, too, was terrifying to an equal extent as a never-ending corridor, extending to the depths of the earth another forty miles or longer.

"Water," said Toph suddenly. "Water is coming." She turned back in alarm. "Something changed in the tunnel up there." She began making motions to one side, then the other, digging out channels. "Aang!"

He moved beside her and took a stance. Even Zuko could hear it then—a large volume of water was moving towards them like a river had been released. Trapped there that far underground, he didn't know if Toph could dig an opening to the surface or not, and if the water reached them, they would drown.

She continued making adjustments trying to form a system to divert the water until the last moment, when from the darkness a tremendous wall of water bore down upon them. Aang grit his teeth and pushed his hands forward, then extended them to either side. The water roared down either diversion channel. "There's too much," he shouted over the deafening roar. "It's like the entire river is coming."

Water began seeping past his hold and swept over their shoes, then calves. In the limited space it rose more quickly than Toph could adjust for. Zuko felt it at his knees and it became difficult to keep standing through the swift current. There were particles and scraps of rivergrass in the flow as well as pebbles and grit. He and Sokka grasped at either wall while the two tried to manage it, but there was no end to the volume. It was not a singular input but a complete redirection of the river into the tunnel, and the river's moving volume exceeded the capacity of the tunnel—in other words, they would be completely submerged if Aang's hold faltered. Zuko kept in his free hand the only flame they had to see by.

Sokka slipped to one knee, swore, and scratched at the wall to stand back up against the water slamming into his torso. Stone groaned as she shifted more aside, and more, but the volume that Aang was holding back was building up more pressure by the second.

Behind them, there was nothing but blackness. If the water hit, they would be dragged underwater down the chute, taken by the current, for such a long distance that they would drown before finding an end point.

"Toph, I can't—" Aang grunted. "Make a wall."

"The pressure would collapse it instantly. I'm doing what I can," she shouted. She cleared more and more stone out around them, but the water continued to flow in. Aang's footing slipped several inches back.

All at once the flow upstream cut off. The remaining water stayed behind Aang's barrier until it was channeled off to the runs excavated at either side. Under their feet the flow diminished, then dried out. Aang released his pose and stood back, panting. The body of water had disappeared.

Toph turned to the side, where she'd dug the diversion channels, and began making digging gestures, leveling out a steep, narrow staircase. "I'm getting out of here. I don't know where that water came from or what stopped it, but that's enough of a tour for me."

As she worked, Aang, using airbending, propelled himself up the channel to where the water had come from, skimming over the ground at an impressive speed. They listened to him go until the sound was blotted out behind the digging. The staircase extended up and up, and she began following it, with her arms sweeping to either side as she increased it step by step. The ceiling was low, and even she was stooped uncomfortably despite being by far the shortest of the group. They both joined behind her, taking the first step warily, and needed to use their hands for support due to the steepness and the low ceiling. It was almost like crawling, but at a sharp upwards angle, unnatural and difficult. Behind them sound impressed from the resumption of the water. Aang darted into the opening then. He huddled on the steps as, below, the water swept down through the channel. It began rising through the staircase, but slowly, more so than her progress upwards.

It extended a disturbing distance and they were still in darkness. Out of immediate danger, they had a moment to breathe, but they were trapped in a small confine, a tight limited opening with the water still rising at their heels, and ahead of them only a dead end of stone. They had to stoop almost to a crawl, as she couldn't open too large of an area without needing to displace too much rock and risk the structure failing.

Aang reported, "I don't know why the water stopped, but whatever caused that pause, it was only temporary. I didn't see any structural change." He was crawling up behind them and kept turning back to check on the progression of the water.

"Almost there," she said, out of breath from the effort. In ten more steps they broke through the surface and braced for what was above.

Dim sunlight and fresh air flowed in. After a tight, unpleasant scramble, they surfaced.

They were in a low area near the beach, a far distance from the village. Had they gone any further they would have been under the ocean. Rounded stones littered the beach and the tide swept between them in gentle waves edged in foam.

Toph crawled to the side and collapsed on her back in a patch of grass. "Not okay. I am not okay with what just happened."

"Anything else that was downstream of us in that tunnel would be flooded now," muttered Sokka. "All the evidence is gone if there was any. And there's no going back in there now."

"Look," reasoned Zuko. "We're way, way out of the village, at the coast of the island. And that tunnel kept going. There is no way someone entered it from underwater. Where else could it have led?"

"Someone had been through there," said Sokka. "I saw the