Disclaimer: All characters are property of ACD, Marvelous Mark Gatiss, Steven "The Moff" Moffat, and the BBC. No copyright infringement intended.
Author's Note: Yes, this is crack!fic. And kid!fic. And a crossover, kind of. And yes, there are deliberate nods to the Cumberbunny's Alan Rickman impersonation and Mycroft!Poppins because I am a meta-reference addict. And I'm getting back to "In the Genes," I promise. It's just that this little detour was irresistibly inspired by sadynax at LJ and her astoundingly adorable pictures of Baby!John/adult!Sherlock and Baby!Sherlock/Adult!John, and who gave me permission to base this story on her art. The cute, it makes my ovaries 'splode.

When The Bough Breaks

by Alice Day

John yawned. God, he was tired.

It was another long day; a half day at the clinic that turned into a 3/4 day with the patient backlog, then clearing up that break-in case at Abbey Road Studios (master digital tapes missing, the substitute sound engineer did it, the Red Hot Chili Peppers were eternally grateful, etc.). And of course Sherlock needed to stop off at Barts afterwards and see if he could cadge yet another body part (fingers this time) from the eminently cadgeable Molly Hooper.

John let him go on ahead, stopping in at a nearby Tesco's to pick up milk and some groceries for dinner. Which turned out to be a bad idea, as one of the carrier bag handles shredded just as he reached the hospital, splitting the bag all the way down one side.

Cursing, he barely caught the milk, bread, spread and cheese before they tumbled to the ground. By the time he got to the morgue, having pulled the bottom of his jumper up and used it as an impromptu carrier bag, poor Molly had actually set out a selection of human fingers for Sherlock's perusal like some sort of cannibalistic cheese tray.

"Don't worry about me. I can handle the groceries," John groused.

Molly didn't even bother to look, although Sherlock gave him a shark-like smile. "I had every faith in you, John," he said. "This may take a while. Why don't you go put the kettle on?"

John tried to scowl, but it turned into a jaw-cracking yawn. Oh, the hell with it—yeah, tea. Or coffee. Or maybe I could just crunch on a handful of espresso beans. While his flatmate mulled over the phalangeal choices on offer, he wandered into the small lounge area of the lab where Molly kept the kettle and tea/coffee supplies.

Depositing the groceries next to the office refrigerator marked FOOD ONLY— I MEAN IT, SHERLOCK, he rinsed out the electric kettle, then refilled it with water. "What d'you two want?" he called.

"Coffee, black, two sugars," Sherlock called back.

"Same for me, but with milk," Molly added.

Coffee it is, then. John opened the fridge, pulling out a full pint jug of Tesco milk. Suddenly he heard frantic footsteps and Molly bolted into the lounge. "Don't touch the milk!" she shrieked.

Startled, John put the jug down on the counter like it was scalding. "Okay," he said, raising his hands. "See, it's down. No milk."

The frantic look subsided, replaced with a smile that would look more at home on the Joker's face. "Hahaha. Sorry. It's just ... I'm on a diet," she said brightly. "So I don't really need any milk in mine, thanks."

He wasn't about to argue with a woman smiling at him like that. "Oh. Um, all right."

Still with that rictus grin, she hustled back into the lab. Alone, John turned back to the counter—

—where two full Tesco milk jugs now sat next to each other.

Oh, bugger. Which one's which? Another yawn overwhelmed him. Oh, never mind. They're both 2%. God, I hope Molly has some spare carrier bags around here.

Blinking, he stuck one bottle back in the fridge and put the other one with his groceries, then finished making the coffee. A quick caffeine infusion, some fingers, and he could finally go home and sleep.

#

Eyes closed, Sherlock stroked the bow over the violin strings, playing a Mozart sonata as he ran through the various permutations of adult human index finger size relative to age and sex.

One of the strings whined, out of tune. He stopped, frowning at the instrument. Odd. The strings shouldn't go out of tune this quickly—

The same whine again, longer this time and drawn out. This time, it was clear it came from upstairs. Sherlock glanced up at the ceiling. 4:37 AM. John could be having a nightmare, I suppose. But he's never made that kind of noise before.

The sound came again, louder. Curiosity piqued, Sherlock put the violin down and headed upstairs, pausing outside John's bedroom door. A soft, wet snuffling noise could be heard inside, followed by a high-pitched wail.

That is definitely not John. It almost sounds like a—

He opened the bedroom door, his eyes adjusting to the dim glow of the streetlights through the curtains. The bed, messy with an old duvet and sheets, seemed to be empty.

He reached back and flicked on the overhead light. No, the bed wasn't empty—it just didn't hold John Watson. Instead, a naked baby boy lay in what looked like John's discarded t-shirt and pajama bottoms, kicking his heels and squealing at the light.

The baby spotted Sherlock, and the squeal softened into a babble. One chubby fist waved, reaching up for the detective. Sherlock ignored it, seating himself at the foot of the bed as he studied the scene.

Firstly, where is John? He didn't come downstairs, and climbing down the side of the building is quite outside his capabilities.

Secondly, why is there a male infant on John's bed, and who placed him in John's usual sleeping attire?

He cocked his head to the side, pale eyes narrowing. The infant has light blond hair, dark blue eyes, a pointed nose and what appears to be a cleft chin. Colouring and facial features are noticeably similar to John's. Hypothesis—the infant is John's offspring, placed on his bed by the child's mother or other relative due to financial or emotional difficulties.

Analysis—the infant is approximately six months old, judging by the fusing of his cranial fossa. Conception would have taken place while John was serving in Afghanistan. Afghani mother unlikely based on child's coloring. Impregnation of a female soldier is possible, except that during Bond marathon John complained of lack of sexual intercourse since 2008. Hypothesis incorrect.

The baby waved his fists again, making a not-unpleasant burbling noise.

Second hypothesis—like many doctors, John served as a sperm donor, and the infant's mother somehow discovered his identity. Similar abandonment scenario.

Analysis—sperm donor scenario possible, but I have been in the sitting room since John went to bed. Impossible for the infant's mother/relative to get up to John's room unnoticed, particularly with crying infant in tow. Second hypothesis incorrect.

He leaned closer to the baby, moving a fold of t-shirt. It revealed a tiny, twisted mass of scar tissue on the baby's left shoulder, as if he'd been shot with the world's smallest gun. Fascinated, Sherlock tugged down the blousing waistband of the pajama bottoms, exposing the baby's legs. Lower down on one chubby, kicking leg was an odd, triangular bruise. It looked exactly like a miniature version of the bruise John sported from colliding with the coffee table yesterday.

A mass of scar tissue and a bruise, in the same place as John's scar tissue and bruise.

John is missing.

An infant that looks remarkably like John, bearing identical injuries, is lying in his bed in his discarded sleeping clothes.

John could not have left the flat without my noticing it.

No one could have entered the flat without my noticing it.

Sherlock sat back, satisfied with his one eliminated the impossible, whatever remains, however improbable, must be the truth.

Final conclusion—somehow, through a yet-as-unexplained process, John has reverted to infant form.

The baby looked up at him, and stopped wriggling. "l'ck!" he gurgled.

Nodding to himself, Sherlock stood up and turned towards the door. "Mrs. HUDSON!"

"There, that's better," Mrs. Hudson said twenty minutes later, as she finished jury-rigging a nappy. "Who's a widdle precious, then?" she cooed.

"Please don't call me that," Sherlock muttered, leaning against the bedroom wall as he glared at the child, now festively attired in a Christmas tea towel, on the sofa.

"Wasn't talking to you, dear," Mrs. Hudson said without missing a beat. "Who'd leave you with a baby, Sherlock? I'm quite fond of you, but I wouldn't trust you with a houseplant, much less a helpless little bundle."

The detective turned his glare on her. "I'm not sure," he muttered. "And that geranium had root rot anyway, plus it helped demonstrate that Mr. Carstairs was poisoned."

"And you never did replace it," Mrs. Hudson continued, picking John up and holding him out to Sherlock. "Take him, dear."

"What?"

"Take him. I'm going back to bed."

Sherlock blinked at the proffered baby, then utilized his best winsome look. "You said it yourself, I can't be trusted with a baby," he said plaintively. "You're a motherly sort. You really should keep him, at least until I determine his origins." Which was the closest he was willing to come to until I figure out what—or who—could have reduced John Watson to a baby.

To his dismay, Mrs. Hudson shook her head. "I'm your landlady, dear, not your babysitter," she said, "and in any case I'm headed off to Blackpool in the morning with Mrs. Turner. Bingo weekend, you know." Gently but firmly, she deposited John in Sherlock's unwilling arms, then headed for the stairs.

"But—Mrs. Hudson!"

She paused. "What, dear?"

This time, Sherlock's plaintive tone was genuine. "What do I do with him?"

His landlady gave him a tired but affectionate smile. "You'll figure it out, Sherlock. You always do."

"I just want you to know this is very tedious," Sherlock said, "and I don't appreciate it at all."

John huffed, bumping his head against Sherlock's collarbone as he gazed in fascination at the laptop screen. It turned out that Dr. John Watson, Infant, didn't care to be put down while Sherlock prowled through medical and research databases. After the third attempt resulted in yet another string of howls and Mrs. Hudson thumping on her ceiling with a broom, Sherlock decided it was ultimately more politic (if not more efficient) to hold John in the crook of his left arm while typing one-handed, searching for answers.

The problem was, there were none. According to current scientific research (including that performed by certain independent groups that considered the Geneva Convention, INTERPOL and the World Health Organization to be nothing but mild annoyances), there was no method of inducing this sort of extreme rejuvenation.

Which simply meant that he'd have to dig deeper, because the alternative—having to raise his flatmate—didn't bear consideration. "Damn it all," he muttered.

The infant in his arm startled, peering up at him.

"Sorry," he added, then rolled his eyes. Oh, that's just ridiculous. This isn't some infant—this is John, a fully grown man despite the current circumstances.

He closed the laptop and pushed it to one side, then lifted John and seated him on the edge of the desk, keeping both hands around the infant ribcage for support. "John, can you understand me?" he asked, leaning closer while keeping his voice low and even. "If you can, give me some sort of sign."

John blinked at him, then smiled gummily and grabbed the first thing he could.

Sherlock sighed. "Yes, John, you have my nose. Kindly release it."

John held on, blowing a contemplative spit bubble. "l'ck."

Watering slightly, the detective's eyes went wide. "Sherlock? You said Sherlock, didn't you?" he demanded. "Say it again—say Sherlock."

"Ga!"

"Sherlock."

"Bbbbbbb."

A full minute of more demands answered by baby babble left Sherlock frustrated and more than a little annoyed. As if mirroring his response, John was starting to blink more rapidly, tiny mouth turning down as he fussed.

"What's wrong now?" Sherlock demanded, lifting up his flatmate and examining the tea towel—dry, thank God. "Are you hungry? Thirsty? I suppose I could make you some coffee. Or is that bad for babies?"

John whined at that, his eyes struggling to stay open. Cautiously, Sherlock lowered the baby until John was semi-sprawled across his chest. With a snuffle, his tiny flatmate shifted in his arms until his head was tucked in the crook of Sherlock's neck, one tiny fist clutching his shirt. His breathing hitched once in a tiny sigh, then evened out as he fell asleep.

"Ah. Well, that makes sense, I suppose," Sherlock said quietly. "Babies are supposed to sleep a great deal, after all. Or is that cats?"

With some care, he sat back in the chair, the warm weight of John on his shoulder held secure with one outspread hand. Obtaining further help would just have to wait until morning. In the meantime, Sherlock mused on the case of the dwindling doctor.

He didn't realize he'd dozed off until he felt two things—a tiny fist enthusiastically tugging on his hair, and something damp on his chest.

He peeled a wriggling John away from his body, grimacing at the stain on his shirt. John's newly downsized body had admirably performed the task that babies were best known for. And when he laid his flatmate on the couch and undid the oversized safety pin that held the tea towel closed, Sherlock's exquisite sense of smell recoiled at the odor that wafted up to greet him.

"Oh, dear God," he muttered, wishing he could breathe through his ears. "That is undeniably foul. I can't say I enjoy the thought of toilet training you, John, so I expect you to cooperate and exercise some self-control in the future, do you understand?"

As if in reply, a yellow stream arced into the air, splattering against his shirt.

"He urinated on me," Sherlock said, his voice laced with utter horror.

"That's what little boys do, Sherlock," Mrs. Hudson replied, still chuckling. "That's why you have to cover their little willies with the nappy while you're changing them."

"Oh."

She'd appeared at the flat's door as soon as she heard his scream for help. "I knew you'd have your hands full, Sherlock, so I just nipped down to the Tesco and picked up some bits and pieces for the baby," she said, already in her second-best coat as she handed over a bulging carrier bag. "And no, I'm not changing him—Mrs. Turner is waiting downstairs in a taxi. Instructions for the formula are on the back of the box, and make sure you wash out the kettle first. Last time I looked, you had goldfish in there." She puttered over and kissed John on the head. "Oooh, you precious thing," she cooed. "I'll be back on Sunday night. Don't let Uncle Sherlock blow you up in the meantime, dear."

The carrier bag contained a pack of nappies, wipes, formula, bottles, toys, and a striped onesie (ridiculous name for a garment, Sherlock thought) that bore a striking resemblance to John's favorite jumper. After reading the instructions on the baby wipe box and the package of nappies, Sherlock gritted his teeth and did what had to be done.

Toilet training, he thought. Definitely a necessity.

At least the onesie was a massive improvement on the tea towel.

After a careful washing of the kettle and more perusing of instructions, a bottle of formula was successfully produced. With some experimentation, Sherlock discovered that the most efficient way to 1) feed John and 2) have full access to his phone and laptop at the same time was to stretch out on the couch, knees bent up, and use them as a backrest for his flatmate, now comfortably seated in the curve of Sherlock's hips. Tiny heels thudded playfully on his stomach as he offered the formula to John, who took it with a happy gurgle.

"If you think people would talk about the swimming pool, imagine what they'd say about this," he muttered, selecting a number he'd cloned from John's phone. "Yes, may I speak to Harry Watson? This is Sherlock Holmes, your brother's flatmate. He—"

He paused, listening to the voice on the other end. "No, he's fine." Sherlock peered at John, who was sucking contemplatively on his bottle. "Well, depending on your definition, anyway. The thing is, John's been caring for an infant, and—"

He frowned at a question from Harry. "Yes, an infant. A baby. One of those little pink things that goes goo. In any case, John's been called away on a medical emergency, so I was wondering if perhaps—"

Yet another interruption. "I don't have the faintest idea who would trust him with a baby, I simply know that someone did and—"

Laughter pealed down the line. "I don't find this funny in the least."

"Well, I don't particularly care what he did to your cat. At the moment, I'm trying to deal with a baby, and—"

His right hand started itching for something to throw. Or John's Browning. "Oh, really? Yes, well, obviously you're too busy polishing off the last of your Newcastle Brown Ale, from the sounds of the bottles. Drinking this early in the morning is doing horrible things to your liver, you know."

There was an abrupt click. "Hello? Hello?"

Sherlock stared at the phone. What a dreadful woman.

"Attempt number two," Sherlock enunciated, selecting another cloned number. Having already texted an excuse that the doctor was ill and wouldn't be in that day, this would take some finesse.

After some faffing about with the receptionist, he finally had Sarah Sawyer on the line. "Yes, hello," he said. "This is Sherlock Holmes, John Watson's flatmate—"

He sighed. "No, he's fine. Good Lord, why does everyone ask me that? He's unavailable at the moment—vomiting copiously, from the sounds of things. Which reminds me, would you be available for some babysitting?"

He closed his eyes as he listened to the response. Truly, I am surrounded by the dull. "Yes, babysitting. I've found myself with a six-month old on my hands, and considering John's current condition—"

Another pause. "Yes, someone entrusted me with a baby. And I would like to fulfill that trust by removing the child from the premises, which are undoubtedly crawling with some sort of hideous bacteria, judging from the sounds emanating from our toilet."

The reply wasn't what he'd been hoping for. "Why not?"

"Oh, for heaven's sake, so you're working, so what? It's a walk-in clinic, not a transplant ward. You handle colds, minor contusions and stomachache. I'm sure the level of care you administer could be just as easily performed by a Capuchin monkey with a bottle of paracetemol—"

There was yet another abrupt click.

He ground his teeth together. Target practice was looking better and better all the time. "Damn it all!"

Another blue-eyed startle. "l'ck!"

He glared at John. "I won't apologize again," he snapped. "Why do you associate with such tedious women, anyway?"

"Bbbbbbbb."

Before Sherlock could bring himself to call Molly and throw himself on her certain sympathies (or, worse, call Mummy and ask for help), his phone pinged:

£1.2M in rubies stolen from Oxford Street jeweler's last night.

Jewels belong to not-so-minor royalty. Home Office is very keen.

Help would be appreciated.

GL

Robbery—boring. Undoubtedly performed by one of the jeweler's employees. Open and shut case, really.

On the other hand, Lestrade has nephews, doesn't he? Surely he knows something about elementary child care?

If he solved the case, then Lestrade would have some free time on his hands. Et voila, one problem solved, at least.

Sherlock peered around the phone at John, who'd finished the formula and was now chewing on his newly-accessible toes.

On the way. Have Donovan pick up packet of banana rusks.

SH

Donovan stood at the entrance to the jeweler's, a Boots bag in one hand and a smirk on her face. "I didn't know you were teething, Freak," she sneered. "Brought a dummy, too, just in case."

Sherlock smiled thinly at the usual insult. "How novel to see initiative from you, Sally," he said. "And I'm not teething, but I suspect he is."

He turned and exposed John, snug in his other arm. The DS's smirk converted into shock. "That's a baby," she said, horrified. "Who in God's name let you have a baby?"

"John's sister," Sherlock lied. "Artificially inseminated, of course. This is John Junior. I'm sure you can guess his namesake. John, say hello to Sergeant Donovan."

"Sa!" John chortled.

"Now, where is Lestrade?"

He tried to push past her, but she stepped into his path. "You can't bring a baby into a crime scene," she snapped.

Sherlock smiled beatifically. "What an excellent point. You are on fire today, Sally. And in recognition of your point—"

He stuffed John into Donovan's arms. "—there. Now I can go into the crime scene."

The sergeant reacted like he'd just handed her a boa constrictor. "Oi!" she spluttered. "I'm not a bloody babysitter, Sherlock!"

"Well, you're certainly not doing anything else useful," Sherlock replied sweetly. "And for God's sake, don't let Anderson anywhere near him. I don't want his IQ lowered any more than it already is. Lestrade?"

As he'd already surmised, it was an open and shut case. The store was a fairly standard layout; large display area in the front, then a hallway that led to a private viewing area, the manager's office, a small walk-in vault, and the employee's lounge and toilet. According to the manager the jewels had been stored in the vault until their owner could retrieve them. There were no fingerprints on the vault door, no damning CCTV footage, no evidence of a break-in. Thus, it was an inside job by an employee (Lestrade had already herded the manager and three clerks into the manager's office, where they waited with a pair of constables) and the jewels were still on the premises. It only remained to figure out where.

Lestrade squinted across the hallway at Donovan and John in the tiny employee's lounge. The sergeant was gingerly feeding him a rusk. "Frozen pop, eh?" the DI mused, before the squint shifted to Sherlock. "No. Too young."

"Too young for what?" Sherlock muttered, peering at the vault's door.

"For you to be the donor. You only met John in March."

The detective tore his attention from the vault, leveling a glare at the grinning DI. "So you're a trained geneticist as well as a detective inspector, eh?" he snapped. "Able to determine parentage with a single glance?"

Lestrade looked taken aback. "I was joking. You're not really—"

"Don't be idiotic—of course I'm not. As you already pointed out, I only met John in March." Sherlock bent closer to the vault door, sniffing it delicately. A pointed smile slid over his face. "Ha. Thought so."

He turned and strode across the hallway to the lounge. The object he expected to see was sitting in plain sight on the plastic table. Scooping it up, he headed to the manager's office, Lestrade, Donovan and a burbling John following in convoy.

Inside the office, a tall, stocky man of West Indian descent, clearly the manager, sat with two young women and one young man. "It's about time," the manager said angrily, "We've been sitting here for over an hour!"

"I do apologize. You'd be surprised how much time it takes to get a baby dressed," Sherlock said brightly, slipping into a cheerful persona. "Gosh, this must be an excellent place to work. Wealthy clientele, excellent security, free coffee and tea in the lounge." He hoisted the container. "And homemade baked goods. Cranberry scones, from the smell." Glee danced in his eyes. "Yummy. Don't you think so, John?"

He held the container out to Donovan and his flatmate, keeping his eyes on the employees until saw the telltale twitch. With a delighted chortle, John grabbed a scone, enthusiastically squashing it. "Woo!"

"Ah," Sherlock purred, peering at John's fist. Liberally coated with scone bits and reddish berries, it also clutched a ruby chandelier earring. "I don't think you'll want to eat that, John." He leveled a thin smile at the male clerk, with the tell-tale trace of flour in his cuticles. "Although I'm sure Mr. Farber will be happy to explain how the jewels got into his scones."

After that, it was the tedious matter of taking statements, hauling the sobbing clerk off to jail, all the boring detritus of modern police work. Sherlock fidgeted impatiently, waiting for Lestrade to finish talking to the stunned manager. Donovan narrowed her eyes at Sherlock, then turned and offered John to Lestrade. "Why don't you hold him for awhile, sir?" she said, pleading in her tone.

"Oh, all right," the DI said with a smile, jiggling John in his arm and beaming at him. "Who's a boy, then? You're a proper detective, you are."

"Of course he is," Sherlock said with some asperity. "He's a Watson, after all. And since he assisted in solving your case, I thought I could call upon you for some assistance in return."

Much to Sherlock's annoyance, Lestrade refused his perfectly reasonable request for babysitting services. "For God's sake, Sherlock, I do have other cases, not to mention a mound of paperwork on my desk that looks like the North Face," the DI said, handing John back to him. "Besides, you already solved the case, so it's not like you're got anything else going on this afternoon. Just wait until John finishes up with whatever he's doing, and you can hand our boy back, eh?"

Oh, Lestrade. Just when I think you have hit a rock bottom low in stupidity, you say something and I discover your underground car park. Scowling, Sherlock turned to Donovan, who stepped backwards. "Don't look at me," she declared, shoving her hands into her pockets.

"Utterly useless, the lot of you," Sherlock growled, settling John in his arm and stalking out of the jeweler's. Behind him, he could hear Lestrade chuckle.

Damn them all.

Back at the flat, after another atrocious nappy change, Sherlock sprawled on the couch with John and continued to sift through medical research data. This time, however, John wasn't hungry, and kept kicking the back of his laptop.

"Stop that," Sherlock ordered. "I mean it, JohOOF!"

His flatmate had wriggled around, neatly kneeing Sherlock in a sensitive location. Grunting in pain, Sherlock thrust the laptop onto the couch back and grabbed John around his chubby middle, pulling him up to chest level. "Don't. Do. That."

John's baby face screwed up. To Sherlock's confusion, he started to cry.

He was the one with an aching testicle, yet John was crying? "What's wrong?" he demanded, fed up with the frustration of the day. "Do you want some more formula? A rusk? Tell me what you want!"

John cowered, bawling even harder. He can hardly tell you what's wrong, can he?

Just then, a memory flashed into his mind, sharp and clear. At nine, Mycroft had owned a wonderful little toy, a blown glass bird with a belly full of red liquid that rocked back and forth at the touch of a finger, bobbing its beak into a small plastic cup of water. The toy was meant to teach principles of thermodynamics, demonstrating the conversion of thermal energy into mechanical energy, but the two-year-old Sherlock simply thought it was wonderful. He'd been told not to play with it, but it was so interesting, and he just wanted to make the silly top-hatted bird head bob.

He remembered reaching out, accidentally knocking it over and breaking it. The red fluid spread all over Mycroft's desk, and then his brother was there, grabbing him up and shouting at him. Sherlock had been so frightened by his brother's sudden anger, he'd burst into tears.

"Oh," he said, softly now. In a perverse sort of way, he was rather proud of himself for figuring out what was wrong. "I didn't mean to scare you, John. You just kicked me in the— well, you kicked me."

He sat up and swung his legs over the edge of the couch, pulling John into the crook of his arm. "It's all right, John. I'm not angry with you. You don't have to cry." After a moment, he realized he was rocking very gently from side to side, murmuring into the silk-soft baby hair. How odd. Perhaps Mummy did that with me. "It's all right," he continued, carefully wiping away tears with his thumb. "Bad Sherlock, frightening you like that. I'm sorry, John. It won't happen again, I promise."

John sniffled and blinked up at him, blue eyes still swimming with tears. "l'ck?"

"Sherlock, yes," the detective agreed. "Silly old Sherlock, and his brave little John."

John tried to smile, but his breath still hitched a bit. Something Sherlock had seen on some ridiculous forensics show came to mind. He had no idea if it would work in real life, but it was certainly worth a try.

He held up his right hand in front of John, gently wiggling the long fingers. "Dancing phalanges," he murmured in a sing-song tone. "Daaaaancing phalanges."

John blinked, his eyes going wide. He grabbed at the fingers and caught two, his mouth drawing down into a tiny O as he studied them.

Sherlock was pleased by John's observational skills. If I do have to raise him, it may not be quite as tedious as I thought. Of course, Mycroft would have to provide a birth certificate, which means working on at least one of his 'little jobs.' But it shouldn't be too bad, and surely I could persuade Mrs. Hudson to babysit, and once John's old enough I'll find one of those bobbing bird dolls—

Belatedly, he realized John had drawn his index finger down, and was now gnawing on it. "Ah," he sighed. "Everything in its own time, I suppose."

The rest of the afternoon was spent with Sherlock's attention divided between internet research on rejuvenation and finding ways to amuse John. It turned out that John thought the Rubik's cube was wonderful to chew on, and he particularly enjoyed it when Sherlock carried him into the kitchen and opened each cupboard, displaying the contents. "Er, perhaps not this one," Sherlock muttered, glancing inside one and spotting his jar of mummified thumbs.

The doorbell rang. "Mrs. Hud— oh, yes, she's off." Sherlock sighed, settling John on his hip and going downstairs to the door. He checked the spyhole and grimaced. "Oh, and now my day is complete."

The door opened to reveal Mycroft, a rather nice baby carrier slung over one arm. "Hello, Sherlock," he drawled.

"Hello, Mycroft," Sherlock drawled back. "Been stealing children again?"

"Don't be tiresome." Mycroft brushed past him, heading for the stairs. "I'd heard about the recent addition to your household. It's dangerous to carry an infant in your arms while riding in taxis and prancing around crime scenes, you know." He hefted the carrier. "This will be much safer for John."

Sherlock glowered. "I'm sure your spy network has provided quite the show," he said nastily, jogging up the stairs. "Really, Mycroft, have you ever thought of taking up a more civilized hobby, such as peeping into women's windows or such?"

Placing the baby carrier next to the couch, the elder Holmes turned and gave the two of them a patient smile. "May I?" he asked, gesturing to John.

Irrationally, Sherlock's arms tightened around his flatmate, turning away slightly. John started to whine a bit.

Mycroft tutted. "Come, now, Sherlock. I won't drop him, I promise."

"If you do, you'll be next." Reluctantly, Sherlock handed the baby to his brother. "John, this is Mycroft," he added. "Feel free to urinate on him all you like."

Mycroft snorted, cuddling John like a born nanny. To Sherlock's private glee, his flatmate didn't look entirely happy. "You already tried that when you were a baby, Sherlock. I know the nappy trick now."

"Ah. Pity."

Mycroft studied John, running a gentle finger along the curve of his chin. "I can certainly see why everyone believed he was Harry's son. The resemblance is really quite striking," he said conversationally. "Most people change rather significantly as they grow older, but Dr. Watson is still recognizable, even as a baby. The eyes, you know." He chucked John under the chin.

Sherlock refused to show any surprise. It made sense that Mycroft would grasp the truth of the situation, instead of dismissing something out of hand for being "impossible." And while it grated on his very soul to ask his brother for help, it was for John. "I've been trying to figure out what happened, but I haven't found anything yet," he admitted. "Have you ever heard of something like this happening before?"

Mycroft frowned in thought, as John burbled and tugged at his tie. "Well, not specifically, but from what I gather, this type of physical transmogrification is usually potion-based," he said. "I suppose a very talented wizard could do it with a spell, of course, but I'm betting our Johnny here drank something he oughtn't."

So much for dismissing the impossible. "Mycroft, has the weight of running the British government finally driven you out of your mind," Sherlock grated, "or are you seriously using words such as 'wizard' and 'spell' in conjunction with what happened to John?"

Mycroft sighed, extracting his tie from between John's gums. "I find I must once again burden you with the inner workings of our government, Sherlock. The usual restrictions pertain, of course. Now, as it happens, magic is indeed a real, functioning force in our world, and is overseen by the Department of Magical Affairs, which is a Cabinet post, as it happens. I believe you even met the Minister once at one of Mummy's Christmas dos. She'd arranged to have you evaluated for their special boarding school, Hogwash or something like that..."

Sherlock didn't believe it, of course. It wasn't until Mycroft had made a call and an ornate envelope in heavy cream paper had dropped down the chimney and started talking to him that he allowed that perhaps his brother wasn't winding him up, after all.

John thought the envelope was terribly funny.

Once Mycroft was gone, envelope stuffed casually into his jacket pocket, Sherlock stalked into the kitchen, examining the crockery, cutlery and other implements scattered across the table and counters. A potion. Right, then—let's see if we can find a magic potion, shall we?

John's teacup from the previous night, still on the counter. But I had a cup of tea this morning with no ill effects.

Potion, AKA liquid based. I took my tea black. John usually takes his with milk.

John bought milk from Tesco yesterday—he brought it into the morgue, grumbled something about flimsy carrier bags, then went off to the lounge to make coffee for us.

And then Molly shouted at him not to use the milk, sounding on the verge of hysteria.

The detective crossed to the refrigerator and opened it, pulling out a pint container of Tesco 2% milk. The same kind Molly uses. I've seen it before in her refrigerator.

"Ma!" John cried, pointing at the container.

"That's what I'm determining, John," Sherlock said. Putting the container on the counter, he twisted the cap off, then leaned over to cautiously sniff at it.

The scent that emanated from the container had nothing to do with milk.

"And we have a winner," Sherlock announced grimly. In his tired state, John must have accidentally taken Molly's milk from the morgue.

Which could only mean one thing.

"MOLLY!"

The assistant pathologist looked up from her microscope. "Oh, dear," she said when she spotted John in his baby carrier, wrapped warmly in an orange blanket. "He did take the wrong milk."

"'The wrong milk'?" Sherlock spat, putting the carrier down on a lab table. "Is that all you can say?"

Her face contorted in worry. "Er, sorry?" she hedged. "It's just that Toby's getting on a bit, and I thought, well, a few extra years wouldn't hurt, and it's not like anyone could tell since he's a cat—"

Pale eyes gone icy, Sherlock advanced on her. "You stupid—"

Squeaking in fright, she stumbled back, fumbling in her lab coat pocket.

"—brainless—"

And pulled out something slender.

"—idiotic—"

"Petrificus Totalis!" she shouted, pointing the wand at him. A bright light flashed, and Sherlock froze in mid-stride.

Behind them, John started wailing angrily. "Oh," she almost moaned, hurrying past Sherlock. "Oh, dear. I'm sorry. It's all right, Johnny, Sherlock will be fine." After a moment, she jogged back into view, a crying John snugged against her shoulder.

"When I dosed Toby with the potion and nothing happened, I thought I'd made it up wrong," she said, patting John's back and doing a side-to-side dance step. "And then I tested it, and couldn't find any of the compounds. I just finished running the tests, otherwise I would've come to see you sooner."

Sherlock remained motionless, but his eyes blazed.

"Er. In any case, I have an antidote. All he needs to do is take it, and he goes back to normal," she said quickly, stepping back and transferring John to her other arm. "Just don't do anything silly, all right?" Pulling out her wand again, she pointed it at Sherlock. "Finite Incantatem."

He staggered forward, sucking in a gasp of breath. "You witch!" he hissed.

"Well, yes," Molly said apologetically. "Surely you'd figured that out by now? I mean, Mum's a Muggle, but Dad's family have been wizards for ages, but I thought being a pathologist was more interesting than working for the Ministry, but I'm a Ravenclaw so I still like to practice my potions just in case, and I'm babbling, aren't I?"

A number of replies bulleted through Sherlock's mind, none of them appropriate in front of a baby. "Give him to me," he said through his teeth, plucking John out of her arms and rubbing circles on his back. John's cries dwindled, softening to a wet snuffle. "He doesn't like to have his back patted."

"Oh. Sorry."

"Antidote, Molly."

Biting her lip, she turned to one of the lab tables and picked up a small serum bottle with a milky turquoise liquid in it, handing it to Sherlock. "Put this in any kind of warm liquid, and get him to drink it. That will return him to his proper age."

"How can I be sure of that?"

"The first potion worked, didn't it?" she said defensively. "And I was at the top of my Potions class. Even my professor said that I had a rare touch, and he never complimented anyone who wasn't in Slytherin."

"Fine. Warm up some milk, and we'll administer it now."

"Oh." She flushed. "Er, I don't think that's a good idea."

"And why not?"

"Well, unless you have a spare set of clothes for him, he's going to be a bit cold on the way home."

Sherlock glared at her, then remembered John's discarded t-shirt and boxer shorts. Unfortunately, she has a point. "All right. Tell me what to do. In detail."

Once again apologetic, Molly outlined how to mix the antidote, administer it to John, and how long it would take to work. Tucking the potion securely into a jacket pocket, Sherlock took John back to the carrier and laid him down, carefully fastening the safety belts and tucking the orange blanket around him. "We will discuss this later," he promised darkly, picking up his flatmate and stalking out of the lab.

Alone, Molly sagged against the lab table. "You even sound like Snape," she muttered.

Back at 221b, Sherlock shook the small baby bottle, thoroughly mixing the warmed formula with three drops of turquoise antidote. "I categorically refuse to call it a potion, John," he said. "Let's just hope this doesn't change you into a lizard or something worse."

John reclined in the crook of his arm, divested of his striped onesie and kicking his feet happily. His dark blue eyes gazed up at Sherlock with an extremely peculiar expression. After a moment, Sherlock realized it was trust.

Complete, utter trust.

The oddest sensation curled underneath the detective's breastbone. For a second, he wondered what it would be like to be that small and helpless again...

...to trust someone like that again...

"Don't be ridiculous," he murmured, finally offering John the bottle. The baby grabbed for it, greedily latching onto the nipple and sucking at the formula. Within minutes, he'd finished the bottle, and was blinking sleepily.

There wasn't much time now. Getting up, he laid John on the couch cushion, belatedly covering him with the orange blanket, and stood back.

John wiggled, stretching his chubby little hands over his head. And continued to stretch. And stretch. His baby body shot lengthways, gaining girth as Sherlock watched in fascination. Limbs lengthened, delicate skin grew ruddier, and fine blond androgenic hair sprouted in the usual places. Within a minute, John Watson was back in his adult form.

Blinking, he opened his mouth. And belched.

Sherlock smirked. "Sorry. Didn't have time to burp you."

"What was it like?"

John took a pensive sip of tea. Redressed and seated in his customary chair, it was like nothing unusual had happened. "Honestly, it's hard to explain," he said. "It was like a very, very weird dream. I knew what was happening, kind of, but I couldn't put it into any sort of logical framework."

Sherlock nodded. "Appropriate. According to psychologists, infants of that age have a limited understanding of the world around them."

"Yeah. And every time I tried to talk to you, I wound up babbling or crying."

"I noticed," the detective said with a wince.

"Sorry." John took another sip of tea. "Although I do remember..."

"What?"

The doctor thought for a moment, then shook his head. "No, this won't come out right."

Sherlock leaned forward. "John, you just reverted to your infant form for a day via a magic potion concocted by someone whom I presumed to be a lovestruck ninny until today," he said. "Nothing you can say will seem odder than that, believe me."

John flushed a bit. "Oh. Well. It's just that ... I do remember when you were, um, holding me," he said. "On your shoulder, I mean, and rubbing my back, or when we were in the kitchen. I remember those bits very clearly, probably because I liked it. Made me feel safe, you know?" He shrugged, staring at his mug with an odd, embarrassed smile.

Sherlock blinked. For some bizarre reason, his brain threw up the memory of a warm, sleeping weight in his arms, and a tiny head tucked into the curve of his neck. "Oh," he said with a cough. "Well, er—"

John waved him off. "I know, I know. High-functioning sociopath, emotions are stupid, all that," he said quickly. "It's just how I felt. I suppose all babies feel like that when they're being held, you know?"

"Hmm," Sherlock said, thinking. "Yes, I suppose they do."

The next morning, John came downstairs, whistling and pulling on his favorite striped jumper as he headed to the kitchen. A quick cup of tea and a check to see if there was anything edible, and then maybe he'd work on his blog—

He stopped at the kitchen door. On the counter next to the sink was the bottle of milk with Molly's potion. An empty cup of tea and the tiny antidote bottle were beside it.

And on the floor, in a tangle of what he recognized as Sherlock's slacks and purple Dolce shirt, sat a solemn six-month-old baby with large grey eyes and a riot of black curls.

He twisted around, looking up at John. "Ga?"

"Oh, no," John moaned. Kneeling down, he scooped up Sherlock, cradling him in his good arm. "What did you do?"

"Ga!" Sherlock waved at the counter.

Standing up with his now-infant-sized flatmate in his arms, John realized his phone had been placed next to the antidote bottle. Kicking the discarded clothes to the side, he moved closer and read the text on the screen:

John: I want to know what it's like. And you're the only one I trust. Give me the antidote tonight. SH

John took in a soft breath. "Why am I not surprised?"

A little hand came up and grabbed his nose in a surprisingly strong grip. Eyes watering slightly, he looked down at Sherlock and made a decision. If they were going to do this, then they were going to do it right—no crime scenes or taxis. There was a park nearby, after all, with swings and a roundabout, and a tiny pond that would be perfect for paper boats, and later that afternoon they could curl up on the couch and watch Thomas the Tank Engine.

He extracted the questing hand, then held it to his mouth. "Om nom nom nom," he growled, pretending to eat it.

Sherlock giggled, a bright sound in the morning air. "Ga!"

John grinned at his flatmate. "Right, then," he said. "Let's get dressed, shall we?"

Fifteen minutes later, Sherlock was snug in a grey onesie and riding John's shoulders as they left 221b. There was the occasional twinge from his bad shoulder, but John didn't mind, especially when he glanced up and saw a tiny finger pointing the way over his head.

Right you are, my lad. The game is on.