This story takes place in the late movie era, between "The Final Frontier" and "The Undiscovered Country", and I imagine Doctor Christine Chapel as having rejoined the crew at that point.

Spock is behaving unusually, and his friends worry. Will they find out the cause of his affliction?

The Sum of Our Parts

Jim started to wonder at their morning briefing if something was wrong. Spock had been two minutes late, and when he had arrived, he had seemed withdrawn and tense.

"Everything alright?" Jim asked.

"I apologize for being late, Captain," Spock answered, "It will not happen again."

"You look a little overworked lately," McCoy said, taking in his pale features.

Spock quickly dismissed his concerns. "I am a Vulcan, Doctor," he said curtly. "I am not overworked."

"You are also half-human, as I have to keep reminding you," McCoy said. "Just do me a favour and give yourself a rest after your shift, overworked or not."

Spock had agreed, and this small issue having been dealt with, they finished their briefing.

Then, they went in separate directions. Jim went to the bridge, McCoy went to sickbay, and Spock went down to engineering to join Mr Scott in testing out a new formula for the optimisation of the subspace bubble at warp speed.

Half an hour into the simulations, Scott was sure he couldn't ignore the unusual behaviour of his superior officer anymore. Being uncommunicative might be in Spock's nature, but he wasn't usually rude.

"This must be a nice change o' routine for you, right?" the engineer asked.

Hunched over the console and programming it for another simulation, Spock frowned. "Will you be quiet, Mr Scott? These are extremely sensitive variables."

Shocked, Scott stood by and watched him key in the formula.

Then, Spock turned towards him and his expression had changed completely. "I am sorry, Scotty," he murmured and bent down to open the console's access hatch.

Mr Scott stared at the Vulcan. First, he snapped at him, now he called him by his nickname? This was definitely not normal behaviour.

Spock fumbled with the opening of the access hatch for longer than normal. Scotty noticed that his hands were shivering and knelt down next to him.

He stopped him with a hand on his arm. "Are ye alright, Mr Spock?" he asked. "Yer lookin' a bit peely wally."

Spock pulled his arm back and said, "I am alright, Mr Scott. I am perfectly fine."

Scotty couldn't help but notice that the last part had sounded more like a command to himself than a truthful answer.

He was distracted by Commander Uhura entering engineering and stood up.

"What brings ye down here, lassie?" he asked.

Behind him, Spock had opened the hatch and commenced rewiring the circuits for another simulation.

"Oh, I'm just between errands and wanted to pop in to make sure you hadn't forgotten our dinner plans for this evening," Uhura said.

"O' course, I haven't. 1800 hours, your cabin."

He threw Spock a worried glance. His head stuck in the access hatch, the Vulcan had started muttering under his breath.

"Is he alright?" Uhura asked quietly.

"I dinnae think so," Scotty said. "But I dinnae know what to do about it either."

Uhura took a step closer to the hatch. "Mr Spock, don't you think you should go to sickbay?" she confronted him.

"And why would I do that?" a muffled voice came from the hatch.

"Because, frankly, you don't seem to be well."

Spock extracted himself from the hatch, slammed it shut and stood up swiftly. He staggered and braced himself against the console.

"Mr Spock, are you alright?" Uhura asked.

Spock shook his head. He had closed his eyes, he was shaking slightly, and his lips were pressed into a thin line.

"Come on, let's get you to sickbay," Scotty said, taking his arm.

"I am fine, I just feel dizzy," Spock protested.

He pushed away Mr Scott's hand, took a few staggering steps away from the console, and promptly fainted, into the engineer's arms.

"Leave it, I'll bring him there myself," Scotty said to Uhura whose hand was hovering over the intercom.

"Are you sure he's not too heavy for you?" she asked as he cradled the unconscious Vulcan in his arms.

"Heavy? The lad's a twig!" he said. "I can take him, but maybe you should alert sickbay that we're comin'."

On the way to sickbay, while in the turbolift, Spock quickly regained consciousness, shocked to find himself being carried by the chief engineer.

"Please set me down, Mr Scott," he mumbled, mortified.

"Alright, but we're going to sickbay, like it or not."

"I'm afraid we will," Spock murmured, as the engineer let him down. He felt in no condition to resist and was shamefully dependent on Scott's help as they walked out of the lift.

Doctor Chapel approached them with a nurse as they entered, Spock leaning onto the engineer for support. They quickly took over and led him over to the nearest biobed, while Scotty returned to his duties.

"Now, what happened, Spock?" Doctor Chapel asked, "Uhura told me you fainted."

"That is precisely what happened," Spock said weakly as he lay down on the bed.

Chapel exchanged a look with the nurse over his head.

Nurse Jenkins, if Spock remembered correctly. She was one of the newest crewmembers, come aboard during the last transfer, having specifically requested the Enterprise. For an instant, something about her seemed eerily familiar, before Spock noticed her haircut. Her blond curls were elaborately pinned up, in a hairstyle that, during the five-year mission had been sported by…

Christine. Christine was asking him a question.

Spock chided himself for his inexplicable lack of concentration and turned his attention to Doctor Chapel.

"Was there something that precipitated your fainting?" she asked with a frown, while Nurse Jenkins turned on the biofunction monitor and examined him with a handheld medical scanner.

"I felt dizzy, nauseous," he said hesitantly, "and I struggled with my concentration."

"Do you have trouble sleeping, lately?" Chris Chapel asked, still frowning slightly.

"Somewhat," Spock said, tight-lipped.

"Do you feel irritable, restless, or anxious?"

"Yes."

Doctor Chapel nodded and cocked her head at him. "You're showing signs of stress, sir. Additionally to what you just described, your heart rate and blood pressure are elevated. I prescribe rest."

Just as she had finished, the Captain entered the ward, and out of the corner of his eye, Spock could see Doctor McCoy approaching them. Just what he had needed.

McCoy took a look at the results of Spock's examination, exchanged a few words with Chapel, and then went over to join Jim at the door, undoubtedly to fill him in on his second-in-command's recent medical development.

"Why is he here?" Kirk asked.

McCoy shrugged his shoulders. "'Cause he's sick."

"Sometimes you're just as bad as he is, Bones."

"Well, I didn't examine him. Chris did," Leonard said, and thrust Spock's report at the Captain. "It's all in here, though."

Jim skimmed the report, and his frown deepened. Stress-related symptoms all over the board. This sounded unlike Spock, but it went along with what he had noticed this morning. Maybe it was time the Vulcan took it easier for a couple of days.

Spock, meanwhile, couldn't help overhearing the conversation happening over his head as Doctor Chapel and Jenkins put away the equipment.

"Have you changed your hair?" Christine asked. "It suits you."
The young nurse laughed lightly. "Thanks, Doctor, I was afraid it'd make me look old. I really like these vintage hairstyles," she said and strode away with the tray of equipment, ignorant to the fact that she had just made her superior officer feel old.

Christine watched her go and sighed exasperatedly. She turned to look down at her patient.

Spock raised one eyebrow and cocked his head, the nearest he could manage to a smirk.

"Now don't you dare say anything, Mister," she hissed playfully. "And don't give me that sassy look."

She helped him up, muttered one last bit about 'vintage hairstyles' and stood back as the Captain and Doctor McCoy joined them.

"I am fine, Jim," Spock began, already standing up.

"Your doctors say otherwise," Jim said and held up his hand to stop the Vulcan's protest. "You'll just have to relax a bit, Spock. Elevated stress levels happen to the best of us."

It would be no wonder, he thought, as he accompanied Spock back to his cabin. The workload had almost doubled in the last few weeks and was winding down only now. He had barely seen Spock outside of work, and, come to think of it, all his friends had noticed that the Vulcan had been even more private than usual. No scientific arguments with Pavel, no dinners with Christine, no evening concerts with Uhura in the rec room, no discussions about his engineering magazines with Scotty, and few to no squabbles with Bones.

They had all assumed Spock was busy with their increased workload, as they all had been. But maybe they had overestimated the Vulcan this time, and the added stress was catching up with him. It still sounded improbable, concerning Spock, but, as Jim liked to remind himself and his Vulcan friend, nothing was impossible.

In his cabin, Spock tried to find some rest. The feeling of nausea had vanished, and he felt more secure on his feet. And yet, relaxing proved difficult and he found himself pacing his cabin. Where was this unrest coming from? He seemed to have difficulties formulating clear thoughts, and when he made himself a tea, he noticed that his hands were shaking. He hadn't even noticed before. He picked up a book and tried to read, but could not muster the concentration needed and found himself rereading a single passage thrice.

Frustrated, he slammed the book shut and put it away, then settled on the bed for meditation. Perhaps these problems, wherever they stemmed from, needed some direct confrontation. He steepled his hands in front of him and closed his eyes. He slowed down his breathing, willing his blood pressure to drop as well. He was a Vulcan, he was in control over his mind, he was in control of his body. Vulcans didn't…

Vulcans didn't doze off. Or so he had thought. He ripped open his eyes to find the chronometer reading five hours later. Five hours later since when? Five hours later than what had happened five hours prior, he thought. But what had happened?

He wiped his hands on his bedclothes. They felt clammy. And why were they shaking? He sat up, staring at his hands. There was something someone had told him to do. He swung his legs out of bed and walked out of his cabin. There was somewhere he should be.

But where? Someone had told him to go back somewhere if he felt worse. He turned right and continued walking. The hallway was curved. If he was walking along a circle, he would arrive somewhere, or come back to from where he had started.

He turned around. Identical doors lined the corridor on both sides. He had no idea which he had come from. But it didn't matter. He had to go somewhere. 'Come back if you feel worse' someone had told him. Worse than when? Was he feeling worse?

He looked down at his feet, carrying him in swift strides. He had fainted, but now he could walk, so he couldn't feel worse.

After a few more steps, he stopped and looked around. Gleaming white walls on either side and no one around, this hallway seemed too empty and big. What an illogical thought, Spock thought, as he leant into a wall. Of course, a deserted hallway seemed empty. He closed his eyes against the artificial light, willing his breathing to calm down. This kind of confusion was unseemly for a Vulcan. He failed at regulating his breathing but pushed off from the wall nonetheless. There was somewhere he needed to be.

He drew a shuddering breath and quickened his steps as he realised that he had no idea where he was or where he was supposed to be.

No, he was on the Enterprise. That he knew. He was on E-Deck, the officers' quarters. He had left his quarters to go somewhere where he was supposed to go if he felt worse.

Maybe he was feeling worse. Logic dictated that if he didn't know where he should go in case he felt worse, he was feeling worse.

He walked swiftly, taking in the signs next to the doors he was hurrying past. So many doors and not a single one meant anything to him.

He stumbled and walked even faster, pushing down the rising panic. He didn't know where to go, and the dizziness had returned so that he had to support himself against the wall while walking. He stared into the hallway curving into the distance. There really was only one way to go.

And then there was a door that meant something. He stopped abruptly in front of the sign, tracing the name with his fingers: James T. Kirk. Jim. Jim would know what to do, he always did.

Spock pushed off the wall and hurried through the door.

Jim Kirk looked up from his paperwork. "Spock?"

His second-in-command remained silent, taking a couple of faltering steps into his cabin while the door swooshed shut behind him.

"Spock, is everything alright?" Kirk asked and stood up.

"Jim…help."

He was shivering and as he moved into the light, Jim gasped. Spock's face was contorted in a pained expression. He looked at Jim with big, brown eyes, and he was stunned for a moment, how human he looked.

"What is it, Spock?" Jim asked and approached him.

Spock grabbed his shoulders so hard it almost hurt. "I don't know what to do," he mumbled, "I don't know what's happening." He frowned, swaying slightly. "Please. Help me."

"I'm with you, Spock," Jim murmured, putting one arm firmly around him, "it's gonna be alright."

"I need to go somewhere," Spock mumbled and leant into him. "I was supposed to come back if I felt worse."

"I'll take you there," Jim said slowly, taking in the Vulcan's exhausted appearance. He was paler even than before, his hair was dishevelled, and he was looking at him with an emotion that could only be described as utter panic.

"It's gonna be alright," Jim repeated softly as he led him out of his cabin. "Come on, I'm taking you back to sickbay."

Once there, Spock was soon subjected to a series of detailed examinations, in McCoy's quest to find what they must have missed earlier today. The kind of emotional instability that Jim had described to him in hushed murmurs when they had come in spoke for an issue going deeper than just elevated stress levels.

When he found something, at last, he had to check the results twice to believe what he was seeing. He had checked Spock down to the microscopic level, and it was in the Vulcan's very DNA that he recognised something was wrong.

"Come take a look at this, Chris," he said, waving over to the younger doctor who had been busy cleaning up a lab table.

"Found something?" she asked, looking over his shoulder.

"You could say so," he grumbled. "Can you do me a favour and take blood and DNA samples from Spock in a couple of minutes?"

"Sure, Leonard," she said, frowning at the lab monitor where the simulation of a Vulcan – human hybrid DNA was shown to become progressively less Vulcan.

McCoy stepped back into the ward and walked over to Spock's biobed.

Jim had refused to leave his side while waiting and rose from a chair as Leonard came over.

"What is it, Bones? What's happening to him?" he asked.

Spock, meanwhile, tried to appear calm and unconcerned, the very fact that his effort was visible a strong indication that he was anything but unconcerned. The Doctor could see the tension in his muscles, and he was rapping his fingers against the side of the bed.

McCoy crossed his arms and frowned down at him.

"Something's wrong with your DNA."

Spock raised one eyebrow in a feeble attempt at humour. "You have said so for the past couple of decades."

"I'm afraid this isn't one of our jokes," Leonard said and sighed. "I wish it was. Part of your genetic information is being suppressed and seems to be on the verge of dissolving."

Spock nodded and averted his eyes, but not before McCoy could see the flicker of frustration pass through them.

"My Vulcan genes, I assume?" he asked bitterly.

McCoy nodded. "Yes. And only your Vulcan genes. Something seems to be targeting them in particular, blocking them, to eventually unravel or even dissolve them." He smiled at Spock in what he hoped was a look of encouragement. "But we'll try to not let it come to that."

Spock ignored his effort. "It's turning me human," he murmured, still not looking at either of them.

McCoy looked at Jim who was either too worried or too shocked to say anything and nodded. "Yes, or at least it tries to remove the parts that are Vulcan."

"Is there anything you can do?" Spock asked. He was looking at his own feet, his hands clenched in frustration.

"Until we know what's causing this, we can only treat some symptoms," McCoy said. "I'll give you a minor tranquilliser and some anti-nausea medication that you can take when needed."

He stepped aside to make space for Dr Chapel who had just entered with a tray of equipment.

"I'm going to take some blood and DNA samples from you," she said while preparing her tools, "to find the root of your problems, and to determine if the unravelling of your DNA is the reason for your difficulties or just another symptom."

She paused as she saw his face. Until now, Spock had never seemed particularly disturbed at a medical diagnosis, but he had swallowed visibly at her use of the word 'unravelling' and was looking at the medical equipment with an air of uncertainty she had never witnessed before.

"Now, don't you worry," she said, adopting a tone she used for very young, and very sick patients. "We're gonna find out what's causing this, and soon, you're gonna feel much better."

He raised an eyebrow at the change in her voice and leant back into his pillow.

"Oh, and until we find out where this came from, stop taking any supplements," she continued, as she was drawing blood from him. "We have to examine the contents of everything you've taken lately."

"Are you saying he might have been poisoned?" Kirk exclaimed, jumping up from his chair.

"I don't want to jump to conclusions," McCoy said grimly as Chapel took the DNA samples, "but something must be causing this plethora of problems, and that cause could be external in its origin. We need to check all his supplements for flaws or even foreign substances."

"Do you think his supplements have been tampered with, then?" Jim asked.

"There's a chance." McCoy looked over at Spock and sighed. "It could be a coincidence, a simple flaw in the fabrication process of one supplement, the cause could be internal after all, a random mutation, but…"

"But?" Jim prodded.

"But the way only his Vulcan genetics are directly affected seems too intentional to me," McCoy said carefully. "I've got a bad feeling about this, Jim. There's a chance he's been drugged, and I don't know why and by what."

"We'll find out, Bones," Jim said firmly and grabbed the Doctor's shoulder. "And we'll start by making sure this is an isolated case and not a ship-wide emergency."
"What are you doing?"

"Checking the food supply system," Jim answered as he moved to the nearest intercom. "Kirk to Chekov."

"Chekov here, Captain."

"I have a job for you, Pavel, a secret mission. There's a chance Spock has been poisoned. I want you to check the food supply system and the kitchen to make sure nothing's been tampered with."

The line remained silent for a moment as Chekov took in this information. Then, he said, "Aye, Captain, I'll see to it myself. Shall I do a security sweep of your cabin as well?"
"Do it, Mr Chekov. Better safe than sorry. Report back as soon as you're finished."

He doubted they would find anything awry in his cabin, but it was regulation.

Spock had listened, and as Christine walked away with her samples and Jim stepped to his side, he propped himself up on his elbows. There was a glimmer of curiosity in his eyes, his scientific strain shining through despite his obvious exhaustion and sickness.

"A drug that suppresses Vulcan genes," he murmured. "Fantastic."

"Fantastic?" McCoy growled incredulously from the foot of his bed. "I know I tell you often enough to indulge your human side once in a while, but this isn't funny. You're unravelling. Literally."

"Bones!" Jim admonished him.

But Spock seemed too preoccupied to pay his outburst any mind. "Funny," he mumbled slowly. "Another F-word. I'm looking for a word. It starts with F."

"I could think of an F-word right now," McCoy said, frowning down at the Vulcan.

Spock meanwhile muttered on, "Fabulous. No. Phenomenal. No, that does not have an F."

Jim bent over him and took him by the arms. "Spock….I think the word you're looking for is 'fascinating'."

Spock nodded. "Ah. Yes. Fascinating." Then his look grew concerned. "I didn't remember, Jim," he whispered.

"I know, Spock. It's alright." Worried by these bouts of confusion, Jim carried on, "How long have you been feeling like this?"

"This bad only for some days," Spock said. "Before, the symptoms were negligible."

"I think that's for me to say," McCoy grumbled. "You should have come sooner."

At least Spock managed to look contrite at McCoy's admonishing tone.

"Can you tell me when me when the first symptoms started to appear?" McCoy asked, frowning down at him.

"It began around four weeks ago," Spock said slowly, clearly concentrating hard, "but it is difficult to say since the symptoms did not all start at the same time, and they have increased in severity since."

He raised an eyebrow at Dr McCoy, who nodded thoughtfully.

"What is it, Bones?" Jim asked.

"Well, it depends. The reason I asked is that I'm worried the changes might be irreversible if he's been exposed to some substance for too long."

He paused to gauge Spock's reaction, but the Vulcan only pursed his lips and listened. This was undoubtedly a thought that had crossed his mind as well.

"That's why we need to find out how long you've been under the influence," McCoy continued, "and the reason you should stop taking your supplements immediately. Assuming the cause of your problems is external, I hope that by stopping to take the affected supplement, your genetics can start rebuilding themselves with the next cell division."

Spock opened his mouth to question the Doctor's use of the word 'hope', but the chime of the intercom distracted them.

"Chekov to Kirk."

"Kirk here. What have you found?"

"Nothing whatsoever, Captain," the young Russian reported. "Kitchen is safe, all food synthesizers Mr Spock could have used as well. Wherever he got it from, it wasn't the food. Your cabin is secure as well."

"Understood. Anything else?"

"Shall I position a guard outside your cabin, sir?"

Jim shook his head, then realised he wouldn't be able to see it. "No, Pavel, better not. If there's foul play, it seems like Spock was the only target, and I don't want to raise suspicion."

"Aye, sir. And sir?"
"Yes, Pavel?"

"Can you tell Mr Spock that if he needs additional help, he can count on me, as well as Uhura, Sulu, and Mr Scott?"

"I'll tell him," Jim said, grinning widely at Spock who had sunk back into the pillow with an embarrassed expression. "Kirk, out."
"Well, seems I'm gonna be burning the midnight oil in the lab." Christine Chapel was standing in the doorway, holding a bunch of hyposprays. She had come in some moments before and had listened to Pavel Chekov's report.

"How long will it take?" Spock asked.

"I don't know yet, until tomorrow, I'd say." She moved into the room and leant against Spock's bed. "I need to check every single supplement you take regularly and examine your DNA, and blood for traces of foreign substances. It'd take less time if I knew what I was looking for, but all I know is something's gotten into your body somehow and is causing all this."

Spock sighed and she smirked down at him. "Don't worry, I am gonna find out, but it's gonna take some time."
"Should I be concerned by how often you tell me not to worry?" Spock asked.

Christine wished he hadn't. With the uncertainty surrounding this case, and not knowing what to look for, or if there even was anything to find, her reassurance was founded in hope more than knowledge. She hoped she would find something, anything. Because if she didn't, the cause of Spock's issues was likely some complex internal problem they had no idea how to fix. But if she did find something, that meant someone had tried to harm Spock, or worse, kill him.

"Are you criticising my bedside manner?" she asked. "And no, don't you worry."

She turned to Leonard, a look of understanding passing between them. They could only wait for the lab results, and make Spock as comfortable as possible in the meantime.

"I'd like to ask you a couple of questions before I release you," Leonard said. "First, are you in pain?"

Spock nodded slowly. "Sometimes. Headaches, muscle pain, and general aches here and there." He sighed and said, "It is difficult to pinpoint."

"That's ok, Spock. Do you feel nauseous?"

"At times. It flares up unexpectedly, but generally occurs when I'm under stress."

"As I thought." McCoy nodded and, turning around to Dr Chapel, said, "Chris, could you prepare…"

"...an antinauseant, minor tranquilliser, and an analgesic, all to be used at our patient's discretion. Labelled and ready to use," she said, holding up the prepared hyposprays one by one.

"I'm gonna lose my job to you again if you keep working at warp speed," Leonard mumbled, beaming at his former protégé. Looking back at Spock, he said, more seriously, "I want you to take the medication as soon as needed, don't wait until you faint or get an emotional overload."

Spock only nodded and accepted the hypos from Christine. He obviously didn't like being reminded of his current emotional vulnerability.

"I believe you know your way around a hypospray," Christine said. "They're labelled. And listen to Leonard."

"Yes, ma'am," Spock said, with a mocking raise of his eyebrow. But the familiar gesture looked tired and listless.

To be continued...

Well, at least they found out what the problem is. Should be easy to fix, then, right?