I've watched Sherlock basically since the beginning, but never wrote any fanfiction for it. Guess what's about to change! I was struck by a ten-ton plot bunny while watching The Sign of Three, and here's the result.

There are some spoilers for The Sign of Three and His Last Vow, so you might consider seeing them unless you want some big surprises ruined.

It was two weeks after John and Mary's happy and eventful union, and Sherlock still couldn't get something out of his head. It wasn't the attempted murder of Major Sholto. Humans tried (and succeeded) at killing each other every day. Yes, the means was creative, but the motive was as old as mankind, and Sherlock had filed it away with every other case he'd taken and solved. It wasn't even the inexplicable bawling from the wedding guests that still played on Sherlock's mind. John had tried to explain sentimentality to Sherlock, and had done the best he'd could.

No, it was Archie, the little boy with the penchant for crime scene photographs.

Sherlock laced his fingers and rested his chin upon them.

Across from him, Archie did the same.

"I want to see the headless nun now."

"Wait until Mrs. Hudson leaves."

Archie glanced at the tea Mrs. Hudson had left on the table two minutes ago. "She's already gone."

Sherlock winked at the boy. Then, moving ever so silently, Sherlock rose from his chair and tiptoed across the room. He grasped the doorknob, turned it, and then flung the door open so violently it banged against the wall.

"Lose something, Mrs. Hudson?" Sherlock asked.

Mrs. Hudson gave a breathless little shriek and fell on her backside. "No- no, Sherlock. I was just-"

"Eavesdropping? Spying? Committing espionage?"

"You don't have to throw the thesaurus at me. I just wanted to make sure-"

"I wasn't corrupting minors?"

"Well, yes, a bit. You've got heads in your refrigerator, Sherlock."

"There's a liver and a set of kidneys in there, too. I won't tell you where I've hidden the appendix."

"He's five years old. His mother will kill you if he goes home and tells her about that refrigerator. She'll probably kill me, too."

"He isn't going to talk; he's not an idiot."

"Then he'll brag to his mates at school."

Sherlock snorted. "He hasn't got 'mates.' The other children think he's defective."

"They don't even know that word, Sherlock."

"They know how to ostracize someone who's cleverer than them."

Mrs. Hudson sighed. "Just don't blow-torch any eyeballs around him. It stunk for days last time you did that."

Sherlock snapped to attention and gave her a military salute. Mrs. Hudson shook her head but turned away and headed downstairs. Sherlock waited until her footsteps faded completely before slamming the door and returning to his chair.

Archie hadn't moved, which even the thickest of adults would have found odd. Here was a boy in a strange house, in a room full of objects that begged to be dropped, broken, fondled, stolen, or possibly ingested, and he'd been left unsupervised. He hadn't even been told to sit still and behave. So why wasn't the room in shambles?

"You are a sociopath."

"What's that?" Archie asked.

"Someone like me."

"A detective?"

"Rarely. Usually the opposite."

"A bad guy?"

"You could be. Like Moriarty."

"Who's that?"

Sherlock strode around the room, grabbing things seemingly at random. A laptop. Folders. Newspaper clippings. A magazine. Photographs held bundled together with paperclips. When his arms were loaded, he returned to Archie and spilled the mess out on the table, where it mingled among the tea cups.

"This is Moriarty." Sherlock handed the magazine to Archie. The cover of the magazine was simple. A man, black hair and dark eyes, wearing the crown jewels. The picture had obviously been taken from security footage.

Archie giggled. "He looks like a king."

"He was, in his own way."

"I like his crown."

"He's dead now."

Archie showed absolutely no reaction. He reached a hand out and touched Moriarty's crown.

"He put a gun in his mouth and blew the back of his head off."

"But he got to be a king first."

Sherlock replaced the magazine with a sheaf of photographs. Archie's eyes lit up. "Is the headless nun in here?"

"No, these are Moriarty's victims."

Archie flipped silently through the pictures. Sherlock watched him intently, waiting to see something cross the boy's face. Shock. Horror. Fear.

Admiration.

"All these people?" Archie finally asked.

"Not directly. Sometimes Moriarty hired people to do it. That first lot, they were poisoned by a very sick man Moriarty paid to kill people. Because it was funny to Moriarty. He liked to make people do awful things," Sherlock explained.

"Wicked. Did Moriarty kill the headless nun?"

"Afraid not."

"This is cooler anyway."

"You're right. Besides being a nun and being headless, there wasn't much more to her. Here there's plots and subplots. A tangled web across continents. Much...cooler."

"Sherlock! Archie's mother's coming in!" Mrs. Hudson yelled from downstairs. "Hide the heads!"

Sherlock gathered up the assorted Moriarty memorabilia and dumped it atop a stack of who-the-hell-knew-what. It was now perfectly camouflaged to any outside observers. After hiding the incriminating photos of dead women and exploded buildings, Sherlock hopped back into his chair and opened the laptop. The screen turned on and a perfectly child-friendly police safety video about not talking on your mobile while crossing the street began to play.

The door opened and Archie's mother took a tentative step into the room. "Boys? Did you have fun?"

"Can I finish watching the police video?" Archie asked.

"Okay, if it's not much longer."

"Only five minutes," Archie replied.

"Headless nun next week, I promise," Sherlock whispered.

"What was that?" Archie's mother asked.

"Oh, field trip next week. We're going to identify pollen from different areas of the city. Invaluable in crime-solving," Sherlock said.

"You're learning so much with Sherlock. You're going to be the most clever boy in class."

"I'm sure he already is," Sherlock said.

The video ended and Sherlock handed over his young associate. "See you next week, Sherlock."

Sherlock closed the door behind Archie and his mother. The detective then lingered, listening to their footsteps. Once he was sure Archie hadn't forgotten anything or his mother wouldn't come back and try to pry, Sherlock returned to the stack of Moriarty articles and crime scene photos.

Only the sneering face of Jim Moriarty had been replaced with the much younger face of Archie. Sherlock grimaced and turned the magazine over, blocking out its cover and every other image of the maniac.

Five Years Later

"What happened to your arm?"

"I broke it."

"How?"

"I was thrown out of a window and landed on a car."

"Did it hurt?"

"I was thrown out of a window and landed on a car."

"You don't have to be sarcastic."

"And you're too clever to be asking stupid questions."

Archie punched Sherlock in the cast and bones set just a day before shifted. Even for someone who'd been beaten, strangled, shot, defenestrated, and generally injured on the job as much as Sherlock, jarring a freshly broken arm was painful enough to make him gasp.

"Don't call me stupid."

"I was calling your question stupid! And I think you've got enough evidence now to know whether or not it hurt!"

Archie glared at Sherlock. Sherlock returned the glare.

"What are you two fighting about?"

Mrs. Hudson, tea tray in hand, stood in the doorway.

"Staring contest," Sherlock replied stiffly. "Set the tea over there and don't distract us."

"You could say 'please' every now and then, Sherlock."

"Fine. Please set the tea over there and please don't distract us."

Instead of doing as Sherlock asked, Mrs. Hudson bustled between Sherlock and Archie and completely blocked their view of each other. "You weren't having a staring contest; you were fighting with a ten-year-old. Honestly, Sherlock, sometimes it's a wonder Archie wants anything to do with you."

Sherlock's mouth fell open. "He started it!"

"I knew it! I knew you were fighting." Mrs. Hudson turned to Archie and gave his head a sympathetic pat. "Don't worry, dear. Sherlock's never known how to act his age."

Mrs. Hudson set the tea tray on the table and, with one more warning glance at Sherlock, departed.

The minute she was gone, Archie gave Sherlock the single smuggest grin the detective had ever seen. Sherlock snorted. "You won't be cute enough to get away with everything for very much longer. Enjoy it while you can."

Archie smacked Sherlock on the cast a second time.

"Mrs. Hudson! He's starting again!"

Five Years Later

Archie was still enjoying it. Sherlock could tell just by looking at him. Puberty hit most children like a freight train, and the results were ghastly; Archie had enjoyed all the benefits of the hormone stew, and had suffered only a brush with the nastier effects. He'd sprung up almost overnight and now stood taller than John, and was quickly sprouting after Sherlock. He had only a few spots of acne on an otherwise handsome face. He'd gone without shaving that morning, but on purpose, because he'd taken the time to comb his hair and otherwise groom. Said hair was still the dark brown of his childhood, though it was now much shorter and tamer.

"I thought you'd forgotten about me," Sherlock said.

"I've been in France with my dad for the summer holiday. I called. Sent texts. Emailed."

"I was on holiday as well. Moriarty locked me in a cage. In an actual dungeon. It took me three weeks to escape. How did I do it?" Sherlock asked. This was an old game of theirs, one Sherlock had started ages ago. He'd go somewhere or do something, usually not something as exciting as being held captive by his arch-nemesis, and then leave subtle clues for Archie to unwind.

Archie stood and began to slowly walk around Sherlock. He examined Sherlock's hands. Lifted the detective's head and none-too-gently pressed on the fading bruises that circled Sherlock's throat. He then squatted down and looked at the soles of Sherlock's boots.

"There were rats involved. You must have picked them up at some point, because those are rat bites on your hands. They're deep, there are a lot of them, but they're all at the same stage of healing."

Sherlock nodded. "I made a lock-pick out of rat bones. The rat wasn't very eager to aid my escape."

"You were caught. A guard or someone put you in a headlock. You kicked him with your right foot. That boot's scuffed but the left isn't. You took the guard's weapon and dealt with anyone else who tried to stop you."

"And how do you know that?"

"Because you have a brain and it's what anyone with a brain would do. And also because the knuckles of your trigger finger are bruised, suggesting you fought over the gun and barely came away with it."

"And how did I return to Baker Street?"

"Stole a car. The keys are in your pocket," Archie said.

"Perfect." Sherlock applauded.

"And what about Moriarty?"

"Did I catch him, you mean? No. Your hero is still out there," Sherlock replied.

Archie fidgeted. "He isn't my hero."

"You've got his hair style. And his five o'clock shadow. If you had the money, you'd have his Westwood, too."

There was no accusation in Sherlock's voice, no hint of anger or betrayal or offense. Simple evidence. Like cat hairs on a jacket or lipstick on a collar.

"He isn't my hero," Archie repeated.

"Your idol, then."

"You're my idol."

Sherlock shook his head. "I was never your brand of sociopath."

"I've been visiting you, learning from you, since I was five years old! If you weren't my 'brand of sociopath' why would I waste so much time with you?" Archie demanded.

"Because I am the best substitute you could find. I was the only one who could understand you. Understand what it felt like to have no friends because all your classmates were gibbons by comparison. To look at your parents and to wonder how that ever produced you. And to look at this, and to see meat."

Sherlock threw the picture of the headless nun on the table.

"And because I could give you this, and it could be our secret. That's why you're really here. Not because after three weeks with your father, you were starving for intellectual conversation. But because you've gone three weeks without seeing anyone separated from their head."

"That's disgusting and you are completely full of shit. I was a kid and I was curious. And maybe a little morbid. A lot of boys are."

"How many little boys pretended to be sick the day Jim Moriarty came back from the dead, just so they could stay home from school and watch him repeat the same four words on every station?"

"How'd you know?"

"'I was worried Archie was coming down with something. He was too sick to get off the couch last week. He seems fine now, though.'" Sherlock upped the pitch of his voice and did a half-decent impression of Archie's mother.

"You remembered something my mother said ten years ago?"

"I remember things the postman said thirty years ago."

Archie drew in a deep breath. "I always did want to meet him. Still do. I'd kill for the chance. Maybe literally."

"I tried," Sherlock said abruptly. He was suddenly out of his seat, pacing. "Tried to interest you in my job. And I did. A little. Didn't I? But collecting dandelion pollen and brick dust wasn't enough. Blood spatter analysis wasn't enough. Flogging corpses wasn't enough. I wasn't enough. I couldn't compete with Moriarty. Or with your genes. So nature and Moriarty win."

"Sherlock-"

Sherlock spun around, his coat billowing out. "I failed. I was inadequate. There is blood on your hands. Left hand, a smudge under the nail of the index finger."

Archie was silent for a moment. "It was a cat. I needed it after three weeks with my dad. It was a cat, or it was him. I chose the cat."

"This time."

"Are you going to tell anyone?"

"Of course not."

"Thank you. I won't do it again."

"No, you will. You'll just wash up better."

"Thanks for the vote of confidence, Sherlock. My mum's probably getting worried. See you next week. If I don't kill anyone by then."

Archie rose from his armchair and without so much as a backwards glance left the flat. Sherlock stayed standing. He wasn't going to tell anyone, not even John. This was his mess, and he had to contain it. If he couldn't, he'd clean it up himself.

TBC