Note: Welcome to this story! This is the first I've written for this particular fandom, so it's kind of exciting.

Just a few notes before we get going. The villain here is an amalgam of three or four real murderers. I became acquainted with their stories, and with the weapon the villain uses, through a Very Weird Job that I used to have. Credit for John's particular skill in this chapter goes to my sister, and enormous thanks go to valmora for talking through the plot with me.

See you at the end! Enjoy!

1. 'Tis The Season

Sherlock knew that John was plotting something even before he opened the door. He could hear John talking to someone as he stood just outside, fumbling in his pockets for his keys. John almost never brought friends or acquaintances home after work, and this break in his routine intrigued Sherlock. He quickly removed the snorkelling mask he had been using in lieu of safety goggles, turned down the flame on his Bunsen burner, and poked his head out of the kitchen, just in time to hear the door open.

John strode into the flat, laughing, followed closely by Mrs. Hudson. "Evening, Sherlock," he said as he entered the kitchen. He carried a small zipped cooler bag, which he popped into the refrigerator, shoving the bowl of spleens aside to make room for it.

"Sherlock, isn't this wonderful?" Mrs. Hudson asked. Her eyes twinkled, and it was child's play to deduce that the contents of the cooler bag were the cause of her excitement. "I knew that good things would come of having a doctor living here with us!"

So. Whatever was in the cooler bag was of medical origin. Had John actually brought Sherlock a little something from the surgery to play with? But then, Mrs. Hudson wouldn't be so gleeful.

"I've brought presents for both of you," John announced. "You'll thank me for this."

"Ah," Sherlock said. "Is this part of the 'manners' you've been trying to teach me?"

"Well, no, not exactly, though I wouldn't mind if you did actually thank me. I meant more that you'll be glad to have it when you see what it is." John considered the kitchen table, cluttered as always with Bunsen burners, test tube racks, microscopes, and other scientific detritus, and pointed to a relatively tidier corner. "Can I have that bit of the table for a moment?"

Sherlock shrugged, and shoved the notebooks and pens aside. John pulled the canister of disinfectant wipes from beneath the sink and swabbed the table. "Mrs. Hudson, if you please?"

Mrs. Hudson pulled a garish William-and-Catherine tea towel from her pocket, unfolded it, and spread it over the table corner, as John pulled one of the kitchen chairs around. He inspected the teakettle for stray biohazards, filled it with water, and took three mugs from the cupboard. "You'll stay for tea afterwards, of course, Mrs. Hudson? We've got PG Tips . . ." He pulled a Twinings tin from the cupboard.

"I shouldn't use that if I were you, John," Sherlock put in. "Unless you prefer arsenic, that is."

" . . . and PG Tips," John finished, a little too brightly, dropping tea bags into the mugs. He then went to the refrigerator and took out the cooler bag, which he unzipped to reveal . . . "Ta da! Flu shots for everyone!"

Quick as a flash, Sherlock retreated to his armchair, where he curled up in a defensive little huddle. "No!" he declared. "You will not! I forbid it."

"Sherlock, dear, it's fine," Mrs. Hudson said. "John said that it's all perfectly safe if we wipe off the table and put down a clean tea towel. Oh, you're too young to know, but when I was a girl, doctors made house calls all the time. You don't get service like that these days."

Sherlock tried to wrap the shreds of his affronted dignity around himself. "Why should you bother me with something as trivial as a flu shot, John?" he asked. "It isn't important."

"Flu season's going to hit hard this year," John said. "We're already seeing the first cases down at the surgery. Everyone there has had shots, and we've got so many that Sarah's allowing us to bring some home for family as well."

"Oh, for God's sake, it's just the flu!" Sherlock snapped. "What's so important? Even if I do get it, I'm young and healthy, a few sniffles and it'll be gone in a week, so there's no need for fuss."

John grinned and shook his head. "Not buying what you're selling. Try two weeks, fatigue and muscle aches in addition to the cold symptoms you just described. You'll be bored out of your mind because you won't be able to go out on cases, and I'll be driven barking mad trying to look after you. Flu shots for all. Doctor's orders."

"Come on, Sherlock," Mrs. Hudson wheedled. "It's just a little stick. You've had a lot worse."

Sherlock scowled at her for daring to bring his real objection to John's attention. "If you are referring to . . . past amusements, Mrs. Hudson, then you should know that I have plenty of first-hand experience with needles. They hurt. Full stop. And there's no reward at the end of a flu shot," he added, almost under his breath.

John looked puzzled for a moment, and then laughed. "Well, of course your needles hurt, Sherlock," he said. "You weren't taught to use them nearly as well as I was. One of the advantages of med school." His eyes took on a predatory gleam. "In fact, I'll bet that I can give you the most painless shot you've ever had. Learned how to do it from a nurse, which is really the only way to learn."

"Oh, really," Sherlock drawled. "Do tell me how you do it."

"Nope. That's your job. You get two chances to observe my technique, and then you can tell us what you've deduced."

He was good, Sherlock had to admit. Despite himself, Sherlock was now interested.

John saw the shift in Sherlock's posture, and hauled him out of the armchair. Mrs. Hudson smiled, removed her cardigan, and sat down in the kitchen chair. "Don't worry, dear, I'll go first," she said. "You'll see, it won't hurt at all."

"Thank you, Mrs. Hudson," John said. He deposited Sherlock in the corner. "You can observe from there." He switched the kettle on and went to the sink to wash his hands. "Now, if everyone cooperates, we'll be done by the time the kettle boils, and we can all have tea."

Sherlock crossed his arms defensively over his chest and watched as John laid out syringes, vials, alcohol wipes, gauze pads, and plasters. He tore open one of the alcohol wipes, swabbed Mrs. Hudson's arm with gallant grace, and then daubed at the area with a gauze pad. He filled one of the syringes, and administered the shot in less than three seconds. Mrs. Hudson smiled at him as he fixed a plaster over the injection site. "That was wonderful, dear," she said. She turned to Sherlock as she pulled her cardigan on. "He's right, you know. It didn't hurt a bit."

She got up from the kitchen chair. John washed his hands again and gestured to Sherlock to sit down. Sherlock did so, silently bemoaning the curse of curiosity that would not let him run away from a puzzle. He kept a weather eye on John as he opened his shirt enough to push it down and expose one shoulder, observing how John opened the second alcohol wipe. The swab was cool on his arm, and John's touch with the gauze was gentle as he patted it dry. John gave him a reassuring smile, filled the second syringe - and in less than three seconds the needle had gone in and out, with no pain at all. Sherlock stared at the pinprick in astonishment as John covered it with a plaster.

"Well done, everyone," John said. He replaced the medical supplies in the cooler bag, put it back in the refrigerator, and washed his hands one last time as Mrs. Hudson picked up the tea towel. The kettle boiled, and then clicked itself off, and Sherlock sucked in a breath as he realized what John had done.

John heard his gasp and smiled. "And well done, Sherlock. Let's get settled with our tea, and then you can tell us all about it."

John did make him wait until they were all ensconced on the sofa, and everyone's cups of tea had been doctored to their satisfaction. It was only after Mrs. Hudson had taken her first sips that John turned to Sherlock. "All right, Sherlock. Dazzle us."

"I've had needles of all different gauges before, so the size of the needle was clearly irrelevant," Sherlock began. "When you said that you had learned from a nurse, well, that can only mean that the secret is in your technique rather than the physical equipment. Your procedure is almost boringly routine, except that you insert an extra stage, where you pat at the disinfection site before you inject the vaccine. Therefore, that must be the trick to a painless injection."

John's face split into a broad grin. "Brilliant, Sherlock! Got it in one. Well, most of it, anyway." He turned to Mrs. Hudson to clarify. "Alcohol disinfects before it dries, and it stings if you put it in a wound. What that nurse taught me was to wipe the liquid off so that the needle won't push any little droplets into the puncture as it goes in."

"Well, would you listen to that?" Mrs. Hudson said. "Isn't it wonderful what you can learn from a doctor, Sherlock? All these years, I thought it was the needle, and here it's the alcohol!"

"Well, it's the needle, too," John said, "though you probably already knew that. Much better to use a needle that's fresh and really sharp. And to do it quickly, in and out."

Sherlock nodded. "I suppose your nurse taught you that as well?"

"Yup. Worked with her on my paediatrics rotation back in school. Got to be fast when you're giving shots to three-year-olds. Came in handy in Afghanistan, too. If it works on a three-year-old child in its mother's arms, it'll work on a nineteen-year-old child in a field hospital. Or, come to think of it, a thirty-five-year-old child in his own kitchen."

"Oh, ha bloody ha."

The doorbell buzzed, and John, who was sitting nearest to the door, pushed himself to his feet. "No, no, Mrs. Hudson, you sit here and enjoy your tea. Be back in a bit." He clattered down the stairs, and Sherlock could hear the door opening and John's voice greeting someone enthusiastically.

"Sherlock!" John called, and then there were footsteps on the stairs again, and John ushered Lestrade into the room. As usual, Lestrade hovered by the door looking vaguely uncomfortable.

Sherlock set his tea down on the coffee table and was on his feet in an instant. "Where is the body, Lestrade?" he asked. "And have you kept Anderson at a safe distance?"

"Er . . . no, not exactly." Lestrade contrived to look even more uncomfortable than usual.

"Brilliant, just brilliant," Sherlock growled. "All the useful information will be destroyed before I even have a chance to look."

"Um, well, sorry to burst your bubble," Lestrade said, "but this time, it's actually John I'm calling for, Sherlock, not you."

That brought Sherlock up short. "John?"

"Me?" John asked, equally befuddled.

"Really?" added Mrs. Hudson.

Lestrade gave a sigh that could best be described as long-suffering. "Yes, really. Yes, John. No, Sherlock, my job does not, in fact, revolve entirely around you."

"What could you possibly need me for?" John asked, just a little bit defensively. "Living bodies are my area. Once they've been murdered, they're Sherlock's."

"Well, that's just it," Lestrade said, clearly relieved to have found a way back to the conversation he had originally intended to have. "We've got a body, but we don't yet know that it was a murder, if you get my drift."

John was silent for a moment. "Ah," he said at last.

"We'd - I'd - very much appreciate it if you could come round and take a look. There's been some pressure on us from the family -"

"And we all know how your skills fare under pressure," Sherlock couldn't resist putting in.

"There's been some pressure on us from the family," Lestrade repeated, a bit more forcefully and with a pointed glare in Sherlock's general direction, "and if it really is a murder, we'd like to get the investigation going as soon as possible, which is why we need your help, Doctor Watson."

"Don't you have people for this?" John asked. "I mean, doesn't Anderson get paid to make these kinds of calls?"

Lestrade sighed. "Anderson called in sick this morning. Got the flu."

John glanced at Sherlock and could not suppress a brief I-told-you-so smirk. "Right," he said. "I'll get my coat. Oh," and he shot a more pointed glance at Sherlock, "and I'm going to need an assistant."

"What?" Sherlock asked, caught genuinely flat-footed.

John pulled Sherlock's coat and scarf off the coat rack and thrust them into his hands. In a low voice, meant just for Sherlock's ears, he said, "Lestrade wouldn't waste his time or ours coming here for a case that he expected to be ordinary, so I'm just going to anticipate things getting very weird very fast. I'll want another pair of sharp eyes on this, and besides, it'll save time explaining the facts to you when things inevitably go pear-shaped. Now, put your coat on and come with us."

"So," Lestrade said, a little awkwardly. "I'll just give you the address and wait for your taxi, then?"

Sherlock opened his mouth to agree, but John beat him to it.

"Not a bit," John replied. "My case, my decisions. We'll save the money and the time and ride along with you. Sorry about the tea, Mrs. Hudson, just leave the cups out, and I'll wash them when we get back."

"Oh, don't worry, dear, just finished the last of mine while you were chatting. I'll take care of things here, just this once since it's an occasion. Not your housekeeper."

"Thank you, Mrs. Hudson. Button up, Sherlock. Lestrade, shall we?" With the gallant efficiency that came when Army officer met medical doctor, John chivvied them out and down the stairs.

"She's going to nose around our things," Sherlock pointed out, probably a bit more waspishly than was strictly called for.

"She's an old lady, Sherlock," John replied. "Let her have her fun."

"As long as she doesn't take my skull again."

"Your skull is safe. I got Mycroft to produce paperwork identifying it as a perfectly legitimate paperweight."

"You did not."

"Did too."

"Have fun at your crime scene, dears!" came Mrs. Hudson's voice floating down the stairs.