"Sherlock?"

Sherlock sighed heavily, rubbing his arm. "What?"

"You keep scratching. Did you get poison ivy again?"

"What?" Sherlock scowled, noting that he was scratching his arm. "No."

"There's calamine in the bathroom."

"I said I don't have poison ivy," Sherlock retorted angrily.

"Okay, fine," John muttered.

Sherlock snorted, flipping through another few pages in the magazine. It took approximately ten minutes for his throat to start tickling again.

Resisting the urge to groan, he tucked his head more again his chest and held the magazine closer.

His throat won out not long after and he pressed his hand over his mouth to muffle the dry cough that had appeared last night.

"Okay, what's wrong?"

Sherlock glanced over at John. The doctor was staring at him; he'd put down his newspaper and was giving him his full attention.

"What's wrong with what?"

"You. You're coughing and, last night, you seemed like you were feeling achy or something. You never stretch. You never make yourself a cuppa during an experiment, never. And you're scratching, again."

Sherlock glanced down; he was indeed scratching his arm again.

"Something's going on, so tell me what."

"There's nothing wrong with me," Sherlock retorted.

"Just let me see your arm."

"No," Sherlock said stubbornly, carding his fingers through his hair and scratching his scalp. The strange phenomena that he was now experiencing was that, since John had mentioned itching and scratching, he was overly conscious of the itching and scratching. Why should it matter if he was scratching? Perhaps Mrs. Hudson bought different laundry detergent. (Even though Sherlock knew that she hadn't, John wouldn't notice.)

"Sherlock."

Sherlock sighed heavily. "Will you stop bothering me, then?"

"Yes," John replied.

"Fine," Sherlock said, grabbing the sleeve of his dressing gown and wrenching it up.

It was much to his surprise as anyone else's to find a rash starting to break out across the expanse of his arm.

"I thought you said you didn't get into poison ivy," John said, standing.

"I should know if I got into poison ivy," Sherlock said, raising his arm to eye level to examine the rash. "And I haven't even been anywhere to get poison ivy..."

He thought back to all of the crime scenes that he'd been at in the past week, week and a half. None of them had so much as a lawn, much less brush. Where could have he gotten into something like poison ivy?

Besides, it didn't really look like poison ivy...

"Doesn't really look like poison ivy," John commented. Sherlock looked at him as the doctor carefully gripped Sherlock's arm to look at the rash himself. "No... but it itches, yeah?"

"Obviously."

"Is there- hang on..." John pulled carefully at the collar of Sherlock's dressing gown.

"What are you doing?"

"There's more on your neck."

Sherlock frowned, raising his hand to rub at his neck. It was a bad decision; it immediately started to itch.

"Are you sure you didn't go near poison ivy?"

Sherlock gave him an annoyed look, fixing the dressing gown's collar before letting his sleeve fall. "I would notice."

He coughed again just then, turning his head to cough into his sleeve.

"Wait, you've got a cough."

"Obviously," Sherlock repeated.

"And I thought you seemed like you were achy last night..." John suddenly leaned forward, pressing his hand to Sherlock's forehead. "You've got a fever..."

Sherlock shook his head, leaning away from John. "I am fine."

"You know what this sounds an awful lot like...?" John mused as Sherlock heard him return to his chair.

"Some inane illness that you think I have, obviously," Sherlock said, returning to his magazine.

"Inane... Well, it is childish; I'll give you that," John replied.

Sherlock could hear the barely concealed humour in his flatmate's voice.

Partly curious, but moreso annoyed, Sherlock once again looked away from the magazine.

"And what is it that you think I'm ill with?"

John smiled innocently. "Chicken pox."

Sherlock paused with his gaze halfway back to the magazine. Chicken pox? John thought that he had chicken pox?

Unfortunately, he had to admit that it seemed to fit the symptoms (that he knew of). He knew that the main symptom of chicken pox was an itching rash. He also recalled that there seemed to be some sort of fever associated with it, but other than that, Sherlock didn't know many of the symptoms. Mycroft had had it once while they had been children, and while Sherlock had deleted most of those memories, he could remember the smug satisfaction of watching Mycroft stumble around the house, covered with itchy red spots.

"Have you ever had chicken pox?" John asked, breaking Sherlock's train of thought.

Sherlock tried to think back. Mycroft had been ill with the chicken pox, Sherlock was sure, but he couldn't remember catching the sickness for himself. Their mum had been overly annoying during that week or so, keeping Mycroft and Sherlock apart as much as she could. Sherlock had been overjoyed; time away from his annoying older brother and his annoying older brother having to deal with the disgrace that was the ridiculous rash.

"Mycroft caught it from high school," Sherlock murmured, "but Mother kept he and I apart during the time that he was contagious..."

"So, you've never had chicken pox."

"I don't think so." Sherlock looked up. "What are the symptoms?"

"The rash and, well, a fever and everything that goes with it. Nausea, dizziness, aches and pains, dry cough..."

Sherlock frowned, his eyebrows knitting together in concentration. If he had chicken pox, where had he picked it up from? He hadn't been around anyone who had chicken pox-

Oh.

A case had taken them to the surgery last week... Perhaps someone had been sick with the illness while he had been there?

"Has anybody been into surgery with this?" Sherlock asked.

"Sherlock, I stopped working there months ago."

Sherlock was barely listening to John, though, seeing as how his mind was racing ahead with the situation at hand. Chicken pox. It was an illness that he had never experienced first hand- not that he ever wanted to experience illness, although he had gotten drunk on purpose once before, for the sake of a case, and the hangover had been sickeningly spectacular- and it was an illness that he knew little about (he knew little about most illness, unless they were deadly).

"John," he said, throwing his magazine onto the table and standing, "where's my laptop?"

John, who hadn't taken his eyes off of him, but who was still smiling like this was some hilarious joke, finally frowned. "Why would I know?"

"No matter," he said, having already crossed the room and picked up John's laptop.

"Sherlock!"

"Be quiet, John; I need to think."

"What? With my laptop? What are you even doing?"

"Research."

"On what?"

"Don't be daft; chicken pox."

Silence ensued for a moment, only broken by the erratic tapping from the keys as Sherlock typed.

John, sounding annoyed, broke it.

"Sherlock, no, this is not an experiment. You need to be resting." John sighed and picked up his newspaper again. "You're going to start feeling a lot worse, Sherlock, and you're going to be forced into resting. Take some paracetamol and absolutely no leaving the flat."

Sherlock dismissed John's words as soon as he heard them, his eyes intent on the computer screen.

Oh, Sherlock's all 'this is Christmas!' right now. John's all 'You're going to realize what a pain this is'. Neither of them are going to have quite the relaxed attitude about it once the illness really starts to bother Sherlock. So, not the common cold, probably a story idea that's been used once or twice, but, the mystery illness has been revealed! (Again, thanks to Storylover18 for the wonderful idea.)

Thanks!