Author's Notes: While I adore Sir Arthur Conan Doyle's original novels and short stories, my heart belongs to the contemporary re-imaginings of Sherlock Holmes. Hollywood's adaptations are incredible, but BBC pulled out all the stops. I've been trying to figure out for ages how to write a non-cliché Sherlock/Harry Potter crossover. But when that failed I decided to utilise the used and contrived plot device of having new tenants move into 221c Baker Street. Thus, this chaos ensued.

General Disclaimer: As I cannot properly use Britishisms, it should be obvious that I'm not J.K. Rowling or Sir Arthur Conan Doyle. This is setting aside the other numerous proofs that I'm neither a famous author nor making any money from this story, but I have plenty of chapters to wax poetic about those.

John Watson stared at his mobile. The text was short, to the point, and gave off a faint air of ominous impatience. The doctor absently wondered if Greg Lestrade had been taking lessons from a certain consulting detective. But then the impact of the words bombarded him and everything else wilted away.

He groaned. Frowning—for this hadn't fully encompassed his sense of imminent doom—he groaned again.

"Bugger." John rubbed his eyes before grabbing his coat, keys and wallet. Reluctantly turning off the lights, he left the comfortable sitting room. "Of course Sherlock didn't tell Scotland Yard he's alive. Course not! A bloody miracle they haven't barged in on a 'drug bust'."

Mumbling disgruntedly he set off down the staircase, wondering where his convenient flatmate had gone and whether or not he had his mobile on him. Yet these thoughts likewise dwindled off in spotting several familiar figures on the stairwell, causing him to shift from heading out the front door to continue descending. Though the doctor at first had hope that some luck had come his way, their spiralling conversation proved otherwise. For though he'd found Sherlock Holmes, the detective's back was to the staircase as he talked to Mrs. Hudson and a few others in front of room 221c.

John paused, letting the conversation wash over him. He noticed that the usually locked door was open wide, and that there was what looked suspiciously like moving boxes and furniture behind it. Further confusion swept over him, for not only did they apparently now have neighbours, but Sherlock was voluntarily talking to them.

"—housing renovation." Sherlock's biting words jerked John out of his musings and back to eavesdropping. Though the consulting detective's harsh tone relaxed him a touch: the new neighbours were being analysed. Everything was right in the world, no impending Apocalypse after all. "An extensive one. There's no issue with money, especially with his job at Scotland Yard. But having both grown up poor you haven't settled into living in a London townhouse, so this temporarily rented flat is more to your liking. Still, having two small children has made this latter impossible for the long-term, especially with her overbearing family and the frequency with which you're pulled into babysitting—"

"John!" Mrs. Hudson cried in welcome relief, derailing Sherlock's familiar habit of 'let's-tell-complete-strangers-their-entire-life-story-for-giggles'. "So glad you're here, come and meet the new neighbours. Harry, Ginny? This is Dr. John Watson. John, Mr. and Mrs. Potter."

"Nice to meet you." John nodded at the young couple ('Whirl-wind romance.' He automatically considered. 'Haunted eyes; the man, at least, has seen trauma') and roughly grabbed Sherlock. The latter had been staring intently at the bemused dark-haired man, barely noticing his flatmate's anger. "Sorry to rush off, but something's happened…"

The red-headed woman—Ginny—smiled in understanding. "Of course, we wouldn't want to keep you. But you should both come over for tea!" As though catching herself she quickly continued speaking. "That is, once we finish unpacking."

"Absolutely." The husband, Harry, absently wrapped an arm around her waist. "We'd have been moved in by now, but 'her overbearing family' has mysteriously disappeared off the edge of—" he caught sight of her raised eyebrow and retreated, "—I mean, yeah, you should definitely come over."

"Thank you." John said with a forced grin, perfectly aware that Sherlock was now staring at the couple as though they'd interrupted him mid-dramatic reveal at the end of a case. "Let me know if I can help with moving boxes or whatnot." With that done the doctor side-stepped Mrs. Hudson and unceremoniously dragged his protesting flatmate up the flight of stairs to the front door.

"What was that supposed to be!" Sherlock protested as they stepped outside. "I was in the middle of a puzzle."

"Hmm?" John looked back and forth on the road, not paying his statement much mind in his annoyance. "How about this for a puzzle. You've been back for two weeks, so why did Greg just text me asking about a rumour that you're a zombie?"

"Greg?" Sherlock asked, peering behind them back to 221 Baker Street. "Ah, Lestrade."

"Yes, him." John groaned as he managed to hail a cabbie. "The Scotland Yard inspector who should've known two weeks ago that you weren't dead!"

"Scotland Yard." Sherlock's eyes narrowed in thought before widening in realisation. "That's it, that's the problem! That was what didn't fit. It's impossible for…John, we're going to Scotland Yard."

"Obviously. No, wait." John stared at him in bewilderment. "Did you hear a word I said? Actually, you know what, I'm not even surprised." A cabbie pulled up as a scraggly haired man leaned out the window. "Scotland Yard, cheers."

"It's elementary." Sherlock steepled his fingers under his chin as their cab pulled away. "Something didn't fit."

John blinked. Stared at his friend, then blinked once more. "We're having two different conversations."

"Then catch up." Sherlock replied blithely, closing his eyes in concentration. "The ring, John. The ring!"

"The what?" The doctor irritatedly asked. "We're supposed to be talking about your not-actual-demise."

"Old news. Hideously boring." A sliver of a smile crossed his lips before his eyes sprang open in excitement. "Her wedding ring wasn't just expensive, it was obnoxiously so. Though at first glance it appeared simple and weathered, the flawless diamond and telling design on the band are things seen on inherited aristocratic heirlooms. The clothes and ring tell of old and powerful money, while his supposed job at the Yard and their clear pasts of money struggles claim otherwise!"

"That's it. I'll stop bothering to ask." John sat back and tried to relax as the cab bypassed Oxford Street. "Silly idea, like you'd tell me what was going on. Also, since when were you an expert on wedding rings?"

"Moriarty!" Sherlock cried triumphantly. "Oh, they are good, aren't they. But their cover is mix-matched in its details."

"Uh huh." John said nonchalantly, staring out the window with feigned disinterest. Sherlock once more frowned in concentration.

"I'm sure it's him." He was now muttering, adjusting his scarf. "Unless this isn't as sinister as first appears."

"Let's go with that." John replied reflexively, wondering if when they got to Scotland Yard he could manage to disappear when Sherlock inevitably got himself arrested.

It was not odd for John to stare at his best friend in disbelief. He'd in fact made an art out of it, and was rather proud of the multitude of incredulous looks he could express at a moment's notice. These stares usually came into being whenever he found that Sherlock had gone even more out of his mind than usual (or was, more times than naught, busy chatting to his blasted skull).

"You think what?" John's jaw gaped with just the right amount of incredulousness, lurking somewhere on the scale between 'you've-gone-mental-because-of-a-fictional-hound?' and 'bloody-hell-ZOMBIE-SHERLOCK!'. "No. No, nuh-uh. Just…no."

"You haven't met them properly." The world's only consulting detective swiftly moved towards the front door of Baker Street, ignoring John's protest of hypocrisy. "Even you would be suspicious. That man is surely one of Mycroft's or Moriarty's. The woman as well, though I admit that the children might be oblivious to the situation."

"Do you even listen to yourself?" John raced after him into the house. "The 'children might be oblivious', my god. I'm sure they're a normal family! You're mental. Absolutely paranoid."

"'Paranoid'?" Sherlock hissed, spinning around in the entrance corridor. "Those people were lying. Everything about them is wrong. If someone hadn't interrupted me I'd have already solved this problem."

"You're an idiot. Greg thought you were a zombie and you should've set him straight from the start." John groaned. "You're lucky he only tried to shoot you. But that's beside the point! There's no problem, no puzzle. They. Are. New. Tenants. Why would they lie?"

"That man is not in Scotland Yard." Sherlock replied abruptly.

The doctor frowned. "Didn't you mention he was a detective? Then how could you tell—"

"Of course he's a detective." Sherlock scoffed, his back turned to their neighbours' door as he stoutly corrected John. "With his automatic surveillance of his surroundings, what else could he be? But he's not Scotland Yard."

"How do you know that?"

"Aside from the fact that he was even slightly observant, unlike the chaps on the force who make even Anderson look intelligent? The records. The police records." Sherlock said heatedly, eyes sparking with what his friend recognised as delight in the newest puzzle. He supposed he should be happy there'd be no bullet hole designs on the wall this evening. "When Donovan fainted and distracted the room, it was child's play to guess Lestrade's password—"

"Sherlock?" John warned, peering over his shoulder.

"—and one search proved that no one matching Potter's name was on the force." Sherlock continued, not paying any attention to his flatmate's less-than-subtle noises to shut up. "He could have told us a pseudonym, but that only increases the possibility that he's in Baker Street for an illegal purpose. That 'wife''s athleticism and flexibility would make it possible that while one was meant for espionage the other was assigned as an assassin. Oho, Moriarty is back! But repeating his tricks? How ordi—"

"HI HI!" A small voice shouted from behind Sherlock, making the latter freeze, halt his monologue, and slowly pivot around to face the now-wide-open doorway to 221c Baker Street. The detective's expression twisted into what on anyone else would have been incredulous surprise.

"Don't mind us." The red-headed woman leaned against the opening of her flat, arms crossed, smirking pleasantly at the two fidgeting men. "You were explaining how my husband and I were sent to spy on and kill someone? Oh, and thank you for the 'athletic and flexible' comment. I thought I'd never loose the baby weight from this little munchkin."

"Hi hi!" Said munchkin repeated, grabbing hold of a speechless Sherlock's leg. John wondered if it was possible to suffocate from pent-up laughter—he supposed there was a first time for everything, but god know's Harry would also die from hysterics if she ever heard about it.

"Don't worry Mr. Holmes, Mr. Watson; I'm harmless." The woman's smirk only broadened as she pulled her excited two year old son off of a stunned Sherlock and carried him back into their room. "Though I can't speak for my husband."

The door shut with a snap behind her.

Sherlock blinked.

John cleared his throat. "Right, yes."

"Not one of Moriarty's then." Sherlock said in a strangled voice, his embarrassment disappearing as he settled back onto the present problem. He pulled John (still somewhat shocked) back up the stairs. "Too blunt. Which means they're here on my brother's orders."

John wrenched his arm from Sherlock's grip and stared, eyes wide in amazement. "They aren't here on anyone's orders! He's an ordinary child—though bizarrely fond of you—and she's a normal woman who luckily found this funny rather than insane. They're a regular family. That's all. There's no case, no puzzle, no mystery."

Sherlock sniffed. "A regular family? Hardly. Wrong, John. Wrong." His expression hardened in excitement as the possibilities swirled through his mind. "Indeed, I suspect that the Potters are as unordinary as can be. How entertaining."

A faint smile graced his lips as he hurried up to the flat, leaving John staring at his retreating figure in bewilderment. Turning slowly, the doctor looked back at the closed door of 221c. He reluctantly conceded that there did seem to be something off…not that it was their business to poke their noses into this. But since Sherlock was clearly going to do it anyway, he might as well tag along.

A/N: This is canon for both fandoms and set post-season two for "Sherlock" and post-Deathly Hallows/pre-Epilogue for "Harry Potter". I intend to stuff as many characters into this tale as possible, so if you want to see anyone in particular let me know!