When Zuko heard emphatic cursing echoing through the temple, he did not expect to find Katara at the source of it.

She sat on the edge of one of the small fountains that dotted the Western Air Temple, facing away from him, a glowing hand held to her mouth. This did little to muffle the blue streak she was expostulating.

The Waterbender dropped the her element with a splash and another hissed curse before taking a deep breath and dipping her hand in the water again and bringing it once more to her mouth. There was a minute of silence in which Zuko observed her furrowed brows and clenched jaw with anxiety, but was broken when she stood suddenly and bent the water into icicles and sent them flying across the room.

"Argh!"

She stomped her foot and fisted her hands in her loose hair. Something that sounded suspiciously like a sniffle escaped her.

The older bender took a small step backwards. He didn't know much about Katara, but he knew if he caught her crying she was pretty likely to explode at him. Unfortunately, his silent getaway was interrupted by a small rock that skittered across the floor, pushed out from under his boot. The Firebender winced.

And, as predicted, the girl whirled on him, her countenance a mask of surprise and discomfort. As she recognised him, a sneer crossed her face.

"What do you want?"

Her voice was acerbic, but her eyes were a little red and something about the way she held her mouth made it seem slightly swollen.

"I – I just – are you alright?"

She gave him a hard glare, presumably trying to see if he was being sincere, though Zuko rather thought that his sudden stammer ought to have been evidence enough of his honesty. He tucked his hands inside his robe and tried to look as inoffensive as possible.

The Waterbender let out a small harrumphing noise, but the tightness around her bright blue eyes disappeared and she suddenly looked much younger. She sat down on the rim of the fountain again with a thump.

"I can't heal it," she said, her voice a strange mixture of plaintiveness, irritation, and a tiny bit of fear.

Zuko blinked. As his mind processed the words, he suddenly understood the fright in her voice: this was the Waterbender who had been able to heal the lightning wound that his sister gave the Avatar – there should be no ailments of the human body that she couldn't fix, given water and time.

"What exactly is it that you can't fix?" he ventured. What kind of disease could it be? How dangerous was it – deadly dangerous? Would it spread to the others – the Avatar, Toph, the Duke? His stomach gave a little clench at the thought of the smallest members of the group he had come to think of as friends and family hurt, with no cure available.

A muscle in Katara's cheek gave a little tic, letting it show the tiniest amount just how much it was costing her to be open with this boy that she still didn't trust. However, she acknowledged to herself, he was the only one she could tell this to. She didn't want to bring anyone that she truly cared for into a situation that she herself was unsure about… but she did need help. And if she had to get it from the Prince of the Firebenders, then that was what she was going to do.

"I don't know," she admitted. "I woke up yesterday morning and my bottom lip was sore and had a lump on it. I thought it might just go away, but now it's swollen more, and painful when I touch it, and it's getting a little bit hard to eat." A line formed between her eyebrows. "And my healing's no good on it. It's to be expected, I suppose. I didn't learn a lot of healing, only the most basic things."

As she was speaking, Zuko had lowered himself to the ground and folded his legs under him, looking up at Katara sitting on the fountain from under his fringe. At her last comment, his head jerked up.

"But you healed Aang after…" He cut himself off and cleared his throat.

"Oh. It wasn't my healing skills that saved him; I used the water from the Spirit Oasis…" Her voiced trailed off awkwardly, remembering what the Spirit Oasis water had almost been used for.

For a minute they inspected opposite walls of the airy room and avoided each other's eyes.

In the embarrassed silence, Zuko racked his brains for the minuscule amount of medical knowledge that his mother and tutors had given him. He tried to slot Katara's symptoms into the diseases and malfunctions of the human body that he remembered, but none of them quite fit, until… His eyes flashed to her face.

"Katara, show me the lump?"

She made a scoffing noise and quirked an expressive brow at him but obeyed, pulling her lip away from her teeth with her fingers and baring the distended flesh to him. The Firebender leaned forward urgently.

What he saw fitted precisely with his suspicions: the area was red and slightly swollen, with an irritated-looking white lump in the middle, just smaller than the nail on his little finger.

The boy leaned back and let out a relieved breath that blew his growing hair out of his face.

"I know what it is, and I know how to fix it." Was it strange that the idea of finally being able to help her to fill him with such giddiness? "Stay here, I'll be back in a moment."

He sprang to his feet at exactly the same time as the look of utter relief swept over Katara's face, and by the time he was at the door it had vanished completely, a politely blank mask had taken its place. Zuko did not see.

The Firebender's footsteps were loud as they slapped against the floor on his return, holding a small oilcloth bag in his hand, the drawstring tightly closed. The Waterbender had rearranged herself so she was sitting cross-legged on the edge of the fountain, and was watching him with curious eyes.

He sat himself on the floor, his shoulders about level with her knees, and proffered the dark red bag on his open palm. Katara looked at it with undisguised interest, then flicked her oceanic gaze to the Firebender expectantly.

"Well?" she asked. "What is it?"

"It's called a mouth-ulcer," the older bender started. "There are other kinds of ulcer, and this is the least serious. They'll eventually go away on their own, but this stuff-" here he pulled open the drawstring with his unoccupied hand and balanced it carefully on her knee "-will speed up the process."

The Waterbender peered inside the bag, which appeared to be full almost to the brim of a fine white powder.

"This," he continued, "is saleratus, which means 'aired salt'. It's also called bicarb by the lower classes, and the sages had their own name for it." He screwed up his face. "Sodium hydrogen carbonate. Or something. It's used often enough in cooking, which makes it quite easy to find. You just need to dampen your finger and stick it in the bag, so the pad of your finger is pretty much covered – yes, like that – and rub it onto the ulcer."

The Water Tribe girl looked askance at her new physician but did as he said – and quickly recoiled.

"That hurts!" she complained. Zuko caught the little bag as it wobbled precariously on her knee and tipped his head back in a nod, saying:

"That's good. That means it's working."

She wrinkled her nose.

"You're not trying to poison me, are you?"

"No!"

The girl shrugged. "If you say so." She gave her fingertip a dirty look but put it back in her mouth, screwing her face up in distaste as she did so.

Zuko hardly believed it. Not that she had suspected him of trying to poison her – he had almost expected that – but that she had so readily taken his word for it that he hadn't. Maybe something good had come of this previously uneventful afternoon. He absently pulled the drawstrings tight again, knotted them loosely, and set the bag on the rim of the fountain next the Waterbender, who was wiping the excess saleratus off her finger onto the pants of her robes.

"Put it on about two or three times a day until it stops hurting – it will probably have healed by then. You can keep that bag, if you like." Here he tipped his head towards the innocuous red bag. "I can get more if I need it."

The Fire Nation boy stood and moved towards the door, where he paused briefly to eliminate a crick in his back. If he hadn't, he wouldn't have heard Katara's sudden call.

"Zuko."

He looked over his shoulder. "Yes?"

"What causes ulcers? And why did you have this on hand?"

He shrugged. "Lots of things can. Too much hot or spicy food, biting the inside of your mouth. It's most commonly caused by stress, though."

The Firebender paused. "I keep saleratus around because I had lots of ulcers as a kid. Generally because of stress." He gave a weak smile. "Spicy food I could deal with. Palace life was a bit harder. I haven't had one since I decided to join the right side of the war, though."

Katara nodded, and Zuko turned to walk away again.

"Zuko."

He turned to look at her once more. "Yes?"

She took a deep breath and summoned a smile. "Thanks."

The Prince's smile was fleeting and barely danced around the edges of his mouth. "You're welcome."

Yes, he decided as he left the room. Something good had become this afternoon, after all.

o0o0oOo0o0o

A/N: Warning! Mega-author's-note ahead!

So, in jubilation at the approaching end of my exams, I sat down and wrote, today. This one was conceived when I found an ulcer of my very own shortly before the English exam. Golly, that made my day. I'm surprised I got anything done in those three hours. Those little suckers are distracting.

Anyway, being me, this gave me an idea for a fic. In a way it makes a lot of sense – everyone would be pretty stressed out at this point after the massive failure that was the Day of Black Sun and having pretty much no clue about how to defeat the Fire Lord, but I kind of thought perhaps Katara would be the one who made everyone else's troubles her own and then try to fix them, in this fic to her own detriment. She just strikes me as that sort of person. And then Zuko would try to help, because he's that sort of person. Also he'd kind of like her to stop hating on his ass quite so much.

But YMMV on all things, of course. :) And on the medical/scientific side of things… I'm pretty much making this up as I go along. The way ulcers and the treatment of ulcers are portrayed in this fic is how we deal with them in our family, and the baking soda thing doeswork! It's just… not what the doctors will give you. And I'm not sure why Katara's healing doesn't work on them, so don't ask. :P

Reviews are better than sliced bread, ladies and gents!

Yours,

~Jo