The pounding on her door came before dawn. It wasn’t the polite rap of an aide; it was a frantic, desperate drumming that jolted Katara from a shallow, restless sleep. She was in her tunic and leggings before the second volley of knocks began, her heart hammering against her ribs with a sick premonition.

“What is it?” she called, pulling the door open to find one of her senior waterbenders, a man named Kustaa, his face pale and grim in the pre-dawn light.

“It’s the aqueduct,” he said, his voice strained. “The third support arch. It’s gone.”

The air was cold on the ride to the site, but not as cold as the dread solidifying in her stomach. From a distance, she could see it—a jagged gap in the rising silhouette of the construction project, a missing tooth in what was supposed to be a triumphant grin. Up close, it was chaos.

A massive section of the aqueduct, a structure of Fire Nation steel and Earth Kingdom stone they had spent weeks raising, lay in a heap of ruin. Twisted metal girders, like the bones of some great fallen beast, jutted from a mountain of shattered concrete and earth. Dust, thick and gray, still hung in the air, coating everything in a fine, gritty film. The air smelled of pulverized stone and wet clay.

Men were shouting. Foremen barked orders that were lost in the confusion. Healers—hers and his—moved through the wreckage, their bending a gentle counterpoint to the sharp, ugly angles of the debris. She saw at least a dozen workers being tended to, their faces streaked with dust and blood. Most injuries looked minor—cuts, bruises, a few broken bones—but the sight sent a fresh wave of nausea through her. This was what she had feared yesterday. This was what happened when speed was valued over sense.

And then she saw him. Zuko was already there, standing near the edge of the collapse, his back rigid. His fists were clenched at his sides, his formal robes already smudged with dust. Even from twenty paces, she could feel the fury radiating from him like heat from asphalt. His people were gathered behind him, a phalanx of soot-stained engineers and workers, their expressions a mixture of shock and sullen anger. Her own people were clustered on the opposite side of the chasm of debris, their faces hard with suspicion. The truce of the previous evening had not just been broken; it had been pulverized along with the concrete.

“What happened?” she demanded, her voice cutting through the noise as she strode toward him. She didn't wait for an answer from him, instead turning to Kustaa.

“The night shift said they heard a groaning sound, then it just… fell,” Kustaa reported, his eyes darting toward the Fire Nation crew. “The steel supports gave way. Snapped clean through.”

A Fire Nation engineer overheard, his face livid. “The supports were sound! We tested every single one. It was the foundation! Your people insisted on using that water-softening technique to set the pylons. You weakened the bedrock!”

“That’s a lie!” one of Katara’s benders shot back, stepping forward. “Our foundations are solid! Your welds are what failed! Rushed work, all of it! Too much heat, not enough care. The metal was brittle as glass!”

The accusation hung in the air, sharp and pointed. Katara’s eyes snapped to Zuko’s. The memory of their fight yesterday—her warning, his dismissal—was a fresh, open wound between them. His jaw was so tight a muscle jumped along the scarred side of his face.

“My welders are the best in the world,” Zuko said, his voice dangerously low. He took a step toward her, his golden eyes burning with a cold fire. “They don’t make mistakes.”

“Everyone makes mistakes,” Katara countered, her voice just as quiet, just as venomous. “Especially when they’re pushed to meet an impossible deadline by a Fire Lord who cares more about schedules than safety.”

His face hardened into a mask of pure fury. The insult landed, direct and unforgiving. He looked from her to the wreckage, at the injured men, and a flicker of something—pain, guilt—crossed his features before being consumed by anger.

“This has nothing to do with the schedule,” he bit out. “This was a structural failure at the base. Your benders were working on the canal diversion less than fifty yards from here all night. Did one of them get careless? Did they saturate the ground until it turned to soup?”

The accusation was so outrageous, so insulting to the precision of her art, that she could only stare at him for a second, breathless with rage. “You think we did this? You think we would endanger our own people, destroy our own work, out of carelessness?”

“I think your methods are untested on this scale,” he shot back, gesturing at the ruin. “And I think you were so determined to prove me wrong yesterday that you’ve become reckless.”

They stood there, separated by a few feet of trampled earth but divided by a chasm of history and mistrust. The shouts of their crews faded into a tense backdrop. All that mattered was the bitter certainty in his eyes and the rising tide of fury in her chest. Yesterday, they had stood soaked in river water, a public spectacle of disagreement. Today, they stood in the dust of a disaster, their animosity now laced with the real-world consequences of failure and the poison of blame. The project was in ruins, and so were they.

A city official, a portly man named Kuan whose robes were already covered in a layer of grime, scurried between them, his hands held up in a placating gesture. “Fire Lord Zuko, Master Katara, please. We must have order. You are the leaders here. You must conduct the investigation. Together.”

The word hung between them, ugly and unavoidable. Together.

Zuko gave a stiff, formal nod, not looking at her. He turned and strode toward the heart of the wreckage, expecting her to follow. The arrogance of it made her teeth ache. With a sharp exhale, Katara followed him, picking her way over splintered timbers and slabs of broken earth. The air was thick with the smell of wet stone and something metallic and sharp, like ozone.

He moved with a predator’s grace, even here, his boots sure on the unstable ground. She watched the line of his back, the tension in his shoulders. He stopped at a massive, twisted girder, a steel beam bent into a grotesque hairpin. It was scorched black in places.

“The main support,” he said, his voice flat. He ran a gloved hand over the surface, his touch surprisingly light. “Rated to hold three times the weight.”

Katara ignored him, her eyes scanning the debris field. Her gaze caught on a smaller piece of fractured metal nearby, a support strut no thicker than her arm. Something about the break was wrong. It wasn't a clean snap, nor was it bent. It was shattered, the edges crystalline and sharp. She knelt, gesturing for a small amount of water from a nearby puddle. It coiled around her fingers before she directed it to wash the dust from the break.

The clean metal underneath told a story. A rainbow sheen of discoloration fanned out from the fracture, the tell-tale sign of metal that had been subjected to extreme, localized heat. Just beyond it, the steel was covered in a network of fine, web-like cracks. It had been heated to near-melting and then cooled too quickly, making it fragile.

“It wasn’t the foundation,” she said, her voice ringing with cold certainty. She looked up at him, her eyes locking with his. “It was the steel. It was made brittle.”

Zuko came over, his shadow falling over her. He crouched down, his thigh almost brushing her shoulder, and she could feel the warmth of his body through her clothes. He picked up the strut, turning it over in his hands. His golden eyes narrowed as he examined the fracture she had cleaned.

“This is one strut out of hundreds,” he dismissed, though a flicker of something unsettled crossed his face. He tossed the metal piece aside; it clattered against the stones with a sound of finality. “A single flaw doesn't bring down an entire arch. It’s not possible.”

“Unless it wasn’t just one,” she retorted, standing up to face him. “Unless it was a pattern. A deliberate weakness introduced into the supports.”

“By who? My engineers?” he scoffed, his lip curling in a faint sneer. “To what end? To see their own work destroyed? To injure their own men?”

“I don’t know,” she admitted, her frustration mounting. “But this kind of fracture… it takes a precise application of intense heat.”

The implication was clear. Firebending.

His face went rigid. “You are accusing my people.”

“I am observing the evidence,” she said, her voice rising.

He turned from her abruptly, his anger a palpable force. He stalked toward the base of what was once the main pylon, the place where the arch met the earth. He knelt again, scraping away loose rubble and dirt with his bare hands, his gloves now discarded.

“Look,” he commanded. She walked over reluctantly, peering down at what he had uncovered. It was the bedrock, the stone upon which the entire structure had rested. It was crumbling, porous and weak. He scraped at it with a fingernail, and small granules of stone flaked away, turning to dust.

“This is water erosion,” he said, his voice a low growl. He grabbed her wrist, forcing her to look, his grip surprisingly strong. Her pulse jumped at the contact. “This is what your ‘softening technique’ did. You leached the minerals from the stone. You turned the foundation of this aqueduct into sand. The entire structure was resting on a lie.”

She snatched her hand back, the skin where he’d held her tingling with heat and indignation. “That’s impossible. Our technique strengthens the surrounding earth. It doesn’t dissolve it.”

“The evidence says otherwise,” he countered, standing to his full height, looming over her. He gestured from the crumbling rock at their feet to the devastation around them. “You wanted to prove your traditional ways were superior. Instead, you destroyed the most important part of this project.”

They stood there, surrounded by the ruin they had both helped create, each holding a piece of the puzzle that fit their own narrative of blame. In his eyes, she saw the unshakeable conviction that her water had eroded his foundation. In her heart, she knew that his fire had shattered her steel. The chasm between them was wider and deeper than the wreckage at their feet, and the truth felt just as buried.

The official, Kuan, wrung his hands, his face pale and sweaty under the midday sun. “Please, a proper inquiry must be held. In the site office.”

He gestured toward a large, drab tent that served as their administrative hub. Zuko gave a curt nod, turning without a word and heading for it. Every line of his body screamed with rigid control. Katara followed, her own anger a cold, hard knot in her stomach. The tent was stuffy, smelling of canvas and damp earth. A single long table and a few rickety chairs filled the space, forcing them into an intimacy that felt abrasive. Zuko took a seat at one end, and she deliberately chose the other, the length of the table a paltry buffer between them.

Their foremen were brought in one by one. Kustaa came first, his weathered face set in grim lines. He stood before the table, his gaze fixed on Katara, pointedly ignoring the Fire Lord.

“Tell us what your crew observed last night, Kustaa,” Katara began, her voice even and professional.

“We worked the late shift on the canal diversion, just as planned,” he said, his tone heavy with implication. “Kept to our side of the site. Not like some.” He cut his eyes toward Zuko. “About two hours before dawn, we heard it. A deep groan. Metal. Sounded like it was in pain.”

Zuko leaned forward, his hands clasped on the table. The movement was slow, deliberate. “What did you see?”

Kustaa’s jaw tightened. He finally looked at Zuko, his expression one of pure contempt. “I saw your men. Two of them. Near the base of the aqueduct, where they shouldn’t have been. Said they were checking the welds one last time.” He almost spat the word. “Looked more like they were admiring their poor craftsmanship before it came down.”

“My men are meticulous,” Zuko stated, his voice flat and cold as stone. “If they were checking welds, it was because they were being diligent.”

“Diligent?” Kustaa’s voice rose. “That structure was built with Fire Nation steel, by Fire Nation hands. It failed. That’s diligence, is it? Or was it something else? A little extra heat in the right spot, maybe? To make a point?”

Katara felt a flush of shame. Kustaa’s accusation was so blatant, so fueled by decades of ingrained hatred. “That’s enough, Kustaa,” she said sharply. He looked at her, his expression wounded, but he fell silent. Zuko’s golden eyes were fixed on her, unreadable but intense, and she felt a sudden, infuriating need to defend her foreman’s prejudice, even as it appalled her. He had lived through the war. He had lost people. His hatred was earned. She dismissed him with a nod, unable to look at Zuko as he left.

Next came the Fire Nation foreman, a burly man named Borin with soot permanently etched into the lines on his face. He bowed crisply to Zuko, then shot Katara a look of undisguised disdain.

“Report,” Zuko commanded.

“The structure was perfect, my Lord,” Borin said, his voice rough. “Every beam, every joint. We finished ahead of schedule, a testament to Fire Nation efficiency.” He paused, letting the barb land. “But the ground beneath it… that’s another story. All night, we could feel it. A softness. A give. The earth was weeping.”

Katara’s hands curled into fists under the table.

“We saw them,” Borin continued, nodding in the direction Kustaa had gone. “The waterbenders. Playing in the mud like children. They were supposed to be diverting the canal, but they were all around the aqueduct’s foundation, pushing and pulling the water through the bedrock. It’s unnatural. Bending the very earth. They turned solid rock into a swamp.”

“That is a gross mischaracterization of a precise and ancient art,” Katara snapped, her control finally breaking. “My benders were strengthening the foundation, not weakening it.”

Borin smirked at her, a cruel twist of his lips. “Is that what you call it? Because from where I stood, it looked like you were drowning the project in your ambition. You couldn’t stand that our engineering was superior, so you washed it all away.”

“Get out,” Zuko said suddenly. His voice was quiet, but it cut through the thick air like a blade. Borin’s smirk vanished, replaced by confusion. “You are dismissed, Foreman.”

The big man looked from Zuko to Katara and back again, then bowed stiffly and left the tent, his resentment radiating from him.

The silence he left behind was heavy and suffocating. The interviews had yielded nothing but ugliness. They had stared into the faces of their own people and seen the war staring back, raw and unhealed. The prejudices they harbored personally were magnified a hundred times in their subordinates, a distorted, hateful reflection.

Katara finally looked at Zuko. His head was bowed, his scarred eye hidden from her. He was rubbing the bridge of his nose, a gesture of profound weariness. For the first time, she saw him not as a prince or a Fire Lord, but as a man burdened by a legacy he couldn’t escape. His people’s blind loyalty was just as venomous as her people’s ingrained hatred. They were trapped, both of them, in a conflict that was supposed to be over.

The silence in the tent stretched, thick and stifling. Katara stared at the empty chair where her foreman had stood, the man’s bitter words still echoing in the canvas enclosure. She felt a deep, weary ache settle into her bones. It wasn't just about a collapsed aqueduct anymore. It was about the war that refused to end, the poison that still seeped from its wounds.

Zuko pushed his chair back with a grating scrape. “There’s nothing more to be learned here.” His voice was devoid of its earlier heat, leaving behind something hollow and tired. He didn’t look at her as he walked out of the tent, leaving her to follow in his wake.

The walk back to their shared quarters was wordless. The sun was beginning to set, casting long, distorted shadows that seemed to claw at the edges of the construction site. Each step felt heavy, an admission of their shared failure. They had been sent here to build a symbol of unity, and in less than a week, they had managed to build a monument to their enduring division.

The neutral space of their diplomatic apartment felt different now. It was no longer just an awkward imposition; it was a container for their mutual resentment. He went straight to a large chest in the corner, the one that held the master copies of the architectural plans. Katara watched him, her arms crossed over her chest. She should have gone to her room, shut the door, and tried to forget the look in Kustaa’s eyes, the sneer on Borin’s face. But she couldn’t. The problem was here, between them, and hiding from it felt like cowardice.

Zuko heaved a thick, heavy roll of parchment onto the low table in the center of the room. He knelt and untied the silk cords, and the scroll unfurled with a dry whisper, covering the entire surface of the dark wood. It was a beautiful, complex document, a fusion of two worlds. The sharp, precise lines of Fire Nation engineering were overlaid with the flowing, spiraling notations of Water Tribe bending forms.

“We’re going over it all,” he said. It wasn’t a question or a request. It was a statement of fact. “From the beginning.”

Katara hesitated for only a second before kneeling on the opposite side of the table. The lantern cast a warm, golden glow over the scroll, illuminating the fine ink work. The space was small. If she leaned forward, her hair would brush his arm. She could feel the heat radiating from him, a steady, physical presence that was impossible to ignore. For hours, they worked in silence, a strange, focused truce settling over them. He would point to a structural load calculation, and she would trace the corresponding water-flow pattern meant to reinforce it. Their arguments from the first day seemed like a distant memory, replaced by this grim, shared task.

It was well past midnight when her eyes caught on something. A small detail in the foundation plans, in a section she had approved herself. It was a pattern for circulating water through the bedrock during the curing process. She’d glanced at it before, assuming it was a standard Fire Nation variant on her own tribe’s techniques. But looking at it now, really looking, it felt wrong.

“This,” she said, her voice quiet. She pointed a finger at a series of interconnected spirals right at the pylon’s base. “This water-flow matrix. It’s inefficient. It diverts nearly twenty percent of the hardening effect away from the central load-bearing point.”

Zuko leaned closer, his head bent next to hers. She could smell the faint scent of smoke and ozone that always clung to him. His good eye narrowed, studying the diagram. “It’s a standard thermal diffusion pattern. It prevents the stone from cracking as it settles.”

“No, it doesn’t,” she insisted, her certainty growing. “Our way, the Water Tribe way, would be to use a single, deep-sinking pulse to temper the core. This… this is just churning the water. It weakens the aggregate. It’s the kind of mistake a first-year student would make.” She looked at him, expecting a defensive retort.

But he was silent, his gaze fixed on the scroll. He was utterly still. Then, slowly, he reached out and slid a different section of the long scroll toward them—the metallurgical annex. His finger traced a line of dense, technical script.

“Alloy composition for the steel support struts,” he read aloud, his voice barely a whisper. “Iron, carbon, chromium… and a trace of copper.” He looked from the script to the water pattern she had indicated, then back again. A muscle in his jaw clenched. “The water here,” he said, tapping the foundation plan, “it’s not just being churned. This specific hydraulic motion, at this specific temperature, would leach the copper salts out of the bedrock.”

Katara’s blood ran cold. She stared at him, understanding dawning in her mind even before he finished the thought.

“Copper salts,” Zuko continued, his voice flat with a terrible discovery, “are highly corrosive to chromium steel. It wouldn’t happen overnight. It would be a slow process. The water would soften the foundation from below, while simultaneously poisoning the steel struts from within. The entire structure was designed to fail.”

He finally lifted his head and looked at her. The animosity was gone from his eyes. The blame, the anger, all of it had been burned away, replaced by the same cold dread she felt pooling in her stomach. This wasn't her mistake. And it wasn't his. It was both, woven together with a malicious, terrifying intelligence. Someone had used their own expertise, their own cultures, as a weapon against them, designing a flaw so perfectly balanced that they would have no choice but to blame each other when it all came crashing down.

The silence that fell was different from the one that had preceded it. The earlier quiet had been thick with blame and resentment. This was a sharp, cold silence, the kind that follows the snap of a trap. The beautiful scroll on the table between them was no longer a blueprint; it was a confession.

Katara felt a wave of nausea. She stared at the elegant, flowing symbols of her own language, twisted into a blueprint for decay. Someone had taken the sacred art of her people, the deep knowledge of water’s properties, and weaponized it. They had turned a technique of reinforcement into a slow-acting poison. It was a profound violation, a desecration that made her skin crawl. Her hand, which had been pointing at the diagram, trembled slightly. She pulled it back as if the parchment were venomous.

Zuko’s stillness was absolute, but she could feel the rage building in him. It wasn’t the explosive, uncontrolled fire she was used to. This was a low, contained burn, the kind that melts steel. He pushed himself to his feet in one fluid motion, turning his back to her and the table. He paced the length of the small room, his boots silent on the woven mats.

“It’s brilliant,” he said, his voice a low growl. “It’s sick, and it’s brilliant.” He stopped and faced her, his golden eye burning with a terrifying intensity. “Whoever did this has access to the highest levels of Fire Nation engineering theory. And they have an academic knowledge of waterbending.”

Katara rose slowly, her legs feeling unsteady. “No,” she countered, her voice shaking with a cold fury of her own. “Not academic. You can’t learn this from a scroll. To know how to corrupt the technique, you have to understand it intimately. You have to know how it feels.”

The implication hung in the air between them. A Fire Nation engineer and a Water Tribe master. Or someone who was both. Or someone who had access to both. The list of potential suspects was impossibly small and frighteningly large at the same time.

“Your foreman was right,” Zuko said, the words sounding like shards of glass in his mouth. “And so was mine. They saw what they were conditioned to see. What the saboteur wanted them to see. Water Tribe ‘magic’ undermining Fire Nation strength.” He ran a hand over his face, the gesture sharp with frustration. “They played us. They used our own history, our own prejudices, against us.”

He looked at her then, truly looked at her, and for the first time since she had arrived, she felt like he wasn't seeing a Water Tribe peasant or a political obstacle. He was seeing an equal. A fellow victim of a meticulously planned attack. The animosity that had been a constant, oppressive weight between them had not vanished, but it had shifted, its focus turning outward.

“This entire investigation,” Katara said, the pieces clicking into place with a sickening finality, “was a performance. We were meant to find nothing. We were meant to fight, to escalate things until the council recalled us both in disgrace. The project would collapse, and the Fire Nation and the Southern Water Tribe would be at each other’s throats again.”

“It’s more than the project,” Zuko stated, his voice dropping. “This is a message. To me. That any attempt at unity is doomed. That cooperation with the other nations is a weakness that will be exploited.”

He was right. The collapsed aqueduct was just the opening salvo. This was an attempt to unravel the fragile peace Aang had fought so hard to build. A chill traced its way down Katara’s spine that had nothing to do with the night air. They were standing on the edge of a chasm, and someone had just tried to shove them in.

The two of them stood on opposite sides of the room, the damning scroll laid out between them like a body. The shared quarters no longer felt like a punishment, but a fortress. Outside these walls, every Fire Nation worker was a potential suspect to her people. Every waterbender was a potential saboteur to his. But in here, for this moment, there was only the cold, hard truth and the two of them against it.

An unspoken agreement passed between them in the charged silence. The fight was no longer Zuko versus Katara. It was them versus the shadow that moved between their people, a ghost of the war they thought they had won. It was a truce born not of forgiveness or understanding, but of a shared and immediate danger. An alliance of necessity. And as they stood there, shrouded in the lantern light, they both knew it was the most fragile, and most vital, alliance of their lives.