A/N: I tried to keep the medical jargon as accurate as possible, though I've almost certainly taken liberties when it comes to procedural matters, i.e. what should be done when. And Barbara would probably know a lot of abbreviations and slang, which I'm forgoing for the sake of readability (and also that sort of thing is hard to research).

Unless people request otherwise, I don't plan on including a glossary of all the terms used in end notes - it will either be (hopefully) clear from context, or else be unimportant in the grand scheme of things.

Except Chapter 2, I will definitely post a list of -ists for that chapter, wouldn't want to get phlebotomist and phrenologist mixed up.

Warning for mild body horror (there's NO gore and NO needles)

On to the story!

It began when Barbara came home from work to the smell of mushrooms and thyme – and a bouquet of other aromas she couldn't place, she lacked the skill – coming from the kitchen, after a tiring day spent mitigating the complications from an unusually difficult appendectomy.

(Later, she would learn it actually began considerably earlier: 2 months, or 16 years, or 1,143 years, depending on how you wanted to measure it. But for her, it began on a drizzly Wednesday night.)

Jim stepped out to greet her, and he was pouting strangely when he welcomed her home and informed her they were having chicken fricassee for dinner. His lower lip protruded, but the rest of his expression remain relaxed and not the least bit sulky. A fat lip? It didn't look swollen…

"Jim, honey, do you have a toothache?"

"What?"

"You're holding your mouth funny."

Startled, he reached up and felt along his jaw. "I am? I hadn't noticed."

Well, that was concerning. "Here, let me check."

He stood obediently still as she used both hands to gently feel along his jaw. She frowned when she felt no swelling, could pinpoint nothing amiss. She had him open and close his mouth several times, feeling the muscles and tendons move underneath her probing fingertips; although his sudden underbite was alarmingly prominent, she could find nothing distended or out of place with the mandibular joint. She checked his lymph glands and his gums, just to be thorough, but… nothing.

"And you're sure you feel fine?" she asked again. "No soreness at all?"

Holding his head in her hands the way she was, she could see the way his eyes flickered, felt a stutter in his breathing as he began to pick up on her own worry.

But then he shrugged, and stepped out of her gentle hold. "None, I feel fine. I'm still not sure what you mean by weird? It's probably nothing… or maybe it will go away on its own."

She stared down at him. Then she took a deep breath to steady her nerves, because she didn't want to alarm him. "Jim, sweetie, I think we need to get you booked for x-rays. And I think you'll see for yourself why I'm… concerned, if you'd take a look for yourself."

"Sounds ominous," he joked weakly, his crooked smile only serving to highlight his misaligned teeth rather than alleviate the growing tension.

The beeping of the oven timer spared her from having to come up with a response, as Jim all too gladly seized upon the distraction and dashed back to the kitchen to turn the stove off. Everything was a flurry of movement, then, getting the table set and serving themselves from the large cookpot.

The food was delicious; the conversation was stilted. At least, it was at the start, when Jim pushed aggressively for normalcy and latched onto topics neither of them had any genuine interest in (the weather. the ongoing construction on Clement Street. what her schedule would look like next week) – short dialogues that quickly petered out when neither had anything more to contribute.

Eventually, they got some conversational traction when she asked how Toby was doing, which somehow lead to a discussion of the latest casting decisions for the next GunRobot movie, and things started to actually feel normal. Which was itself surreal. She felt as though a rug had been pulled out from underneath her feet, and she'd barely managed to keep her balance. But Jim needed her to be strong. Jim needed her to be the doctor who knew the answers and who would make everything be alright. So she could – would – make it through this dinner without staring constantly at his mouth.

And she even thought she would have succeeded in this goal, if it weren't for the fact that the strangest thing of all was how little trouble Jim seemed to be having chewing. She would have expected him to need to cut the food into small, swallowable pieces, or else to struggle with teeth whose relative positions had flip-flopped. Instead, his incisors had no difficulty shearing off pieces of food to masticate with molars similarly unencumbered.

Jim almost certainly noticed her attention, but he was too polite to say anything, until finally they were both finished eating, and he pushed back from the table. "I uh, I gotta say, I'm really curious what's up with my mouth." He rubbed one hand along his jaw. She wondered how his hand could fail to register something out of place. "But from the way you were staring, I'm starting to feel the anxiety – just a little bit!" he hastened to reassure her, looking a bit panicked at the thought that he'd implicated Barbara in giving him anxiety.

"Do you want me to come with you?"

"what? No, god no. I don't need you to – I can go look in a mirror by myself, it's not… ugh." He threw up his hands in exasperation. "Thanks, but I'll be fine."

"I'll clear the dishes, then, and if you change your mind…"

He waved a hand in acknowledgement as he turned and headed up the stairs. Barbara got started cleaning up from dinner, working as quietly as she could and keeping her ears peeled. Several long, silent moments passed, and just as she was putting the last glass into the dishwasher, she heard a thump from upstairs.

In an instant, she found herself at the foot of the stairs. "Jim, honey, you alright?" she called out, debating whether Jim would find it smothering if she went up after him. Just as she decided she would at least go up and wait outside the door, Jim came out of the bathroom and looked down at her, frozen on the bottom step with one hand on the banister.

He was looking a little wild-eyed and spoke in a small voice. "um, yeah, x-rays sound good."

She held his gaze for a long moment, trying to convey as much love and support as she could. "I'll make some calls."

Barbara took a moment to collect herself before she knocked on Jim's door, carefully leveling out her expression until her calm, collected, best bedside-manner face was firmly in place, with none of the roiling emotions she was experiencing visible. (Jim might recognize her mask for what it was and resent her choice, but it was still better than the alternative.) Two sharp taps on the door, and at Jim's acknowledgement she walked in. Her son was in the process of sitting up, having clearly been lying prone on the bed a moment earlier.

"I had to pull some strings, but I was able to get you an appointment with Dr. Jansson tomorrow, she's an excellent radiologist."

"Mmhmm," he hummed noncommittally. She walked forward to sit down next to him on the bed, and he swung his legs over the side to make room. "I talked to Toby. He has more experience with teeth problems than I do."

"Did he have any advice?"

"Not particularly. Just, like, follow whatever instructions I am given to the letter. And he gave me the number to his orthodontist."

"Sounds like he's got your back. And you know I do as well; whatever this is, we'll figure it out, together."

"I know, Mom. I know."

She wrapped one arm around him, deep in her own thoughts. Whatever was going on with Jim, it wasn't causing him physical distress. And it probably wasn't anything life-threatening, she told herself very, very firmly. But what it was, was Unknown, and unaccountably strange.

She kissed him goodnight and retreated to her own room, where she lay awake for hours.

A/N2: Back in the writing saddle after 2 years of not posting anything, Whoo! (Apologies to anyone who started following me years ago when I wrote Flash fic. Although I have several half-finished drafts for new one-shots of 'Inertia' and 'Internal Affairs,' at this point in time they are highly unlikely to be completed, as I'm not active in the fandom or up-to-date with the show.)

In researching bone growth for this fic, I looked up replacement rates for various tissues, e.g. how long before every cell in our skin is replaced, how long to replace all our red blood cells, etc. And part of me wanted to use that timeline for Jim's transformation, like if he hit a point in his development where his body stops making human cells. All the living cells his body currently has still exist, but when they copy their DNA to divide, they copy a previously-dormant strand of troll DNA. So all new cells going forward will be troll cells.

His stomach lining would be replaced in a matter of days; all his red blood cells in ~5 months. Osteoblasts (bone cells) would take 10 years. Interesting food for thought, but ultimately not viable with the story I already had sketched out, so I disregarded the relative rates.