Please forgive this. The plot bunny wouldn't leave me alone.

"Make my wish come truuuuuuuuueeeee..." Harry sang at the top of her voice, stumbling out of the cab in front of 221B Baker St, a "reindeer antler hat" made of tin foil perched on top of her sandy hair.

A pale, trench coat clad man followed her out, wearing similar head gear and looking equally tipsy. "All I want for Christmaas is yoooooooooooooouuuuuuuu!" He finished in a pitchy falsetto.

Finally, John payed the driver and exited the cab as well, looking exhausted. It was funny, he thought grimly, how last year he'd spent Christmas Eve removing shrapnel from a friend's chest in an unsterile environment where any minor slip of the hand could have proven fatal, and he'd been more at ease then than he was now.

Of course, there was no way he could have known the evening would turn out like this. Sherlock had returned home early from Christmas dinner with Mycroft and their mother - another family argument, John guessed - just as John was about to go out with Harry for drinks. He'd hated the thought of Sherlock being alone on Christmas Eve, and invited him along, a little surprised when his prickly flatmate accepted the invitation and even more surprised when he'd drank nearly as much as Harry over the course of the evening.

Now the two were absolutely smashed, wearing matching tin foil hats and singing bloody Mariah Carey Christmas songs all the way home. They looked about ready to either pass out or vomit. John sighed, pulled Harry's arm over his shoulders (she looked the more unsteady of the two), grabbed Sherlock's sleeve and carefully guided them upstairs.

"Good Kind Wenzel lost his snout on the beast of evenin'" Harry slurred quietly.

"I'm sure he did." John muttered.

He released Sherlock's arm, hoping the detective wouldn't topple over left to stand on his own, and set Harry down on the couch, placing a pillow under her head and covering her with a blanket.

"'Night Harry." He said softly. "Please try not to vomit on the furniture."

"Johnny..." she murmered into the pillow. "Is Santa coming tonight?"

John rolled his eyes. "Not if you don't go to sleep, he isn't. Goodnight, Harry."

She was asleep - or unconscious - before he finished speaking. One problem down, he turned to the inebriated sleuth behind him.

"Alright, Sherlock, time for bed... Sherlock?"

When John had left him to tend to Harry, his flatmate had been wobbly and giggly, with a not-all-there look on his face. Now, he was standing there, steady as he ever was with a serious expression, the normal sharp look back in his eyes.

"What the-"

"I thought she'd never pass out." Sherlock said, seeming annoyed. "She can ceratinly hold her liquor, that one."

"Years of experience." John said dryly. "Hold on- what? How are you-?"

"Sober? Really, John, I thought you'd been paying more attention at the pub. I never actually drank anything at all. I just acted the part. Your sister's antics did help, though, as I was really only mirroring what she did."

John stared at him incredulously. "It was all an act, then? The singing? The tin foil hats?"

"Oh, no. The hats serve a purpose." Sherlock said, as if it were the most obvious thing in the world. John gave him a blank look, and he grudgingly elaborated. "I'm on something of an investigation tonight, John." he said.

John rolled his eyes. "On Christmas Eve? I thought even you might be willing to take a break-"

"It's a long-term investigation." Sherlock interrupted. "With years spent gathering evidence, all centred around this night. Tonight, I intend to prove my hypothesis."

"Which would be...?"

Sherlock motioned for John to come closer, out of any possible earshot of his slumbering sister. He whispered conspirationally, as if paranoid.

"Every year, for nearly a decade now, Mycroft has put on copious amounts of weight starting mid-October. He says it's due to stress. He loses it every year, apparently as a New Year's resolution. He also every year initiates an argument over Christmas Dinner at precisely 5:00 pm, usually bringing up something illegal I've done in front of Mummy. This upsets her and causes an argument that invariably ends up with us parting at 5:15 pm. Mycroft then disappears, completely off the radar, and will not respond to any texts or calls I happen to place to him. He even cuts off his surveillance on me, which I proved three years ago by staging an abduction. Also, he stops shaving roughly three weeks before Christmas and pays close attention to coal-production in foreign nations."

"So, weight gain, leaving early on Christmas Eve, growing a beard, and... coal?" John's face took on that oh so familiar incredulous expression of his as Sherlock's conclusion took shape in his mind. "Sherlock, you can't be serious."

"Do I look like I'm joking?" Sherlock said seriously. "I have thought of every other solution that resolves all facts, and everything else has been impossible. So, logically, when you've eliminated that, whatever remains, however unlikely it is, has got to be the truth."

"So you're saying that-"

"Right. Mycroft is secretly Father Christmas."

John stared at him for a long time before speaking. "Are you sure you've had nothing to drink?"

"John-"

"Right, I'm off to bed."

"John!" Sherlock hissed as the shorter man turned away. "Come on! I need you!"

John sighed and turned back around. "For what, some sort of stakeout? Let's just say for argument's sake this crackpot theory of yours is true. If Myrcoft is really... Father Christmas, he's not going to waltz into our flat when we're awake."

A delighted smile crept over Sherlock's features. "Ahh, you're right. But that, John, is where the tin foil hats come in. I suggested the idea to your sister while you were outside calling Sarah. she thought the idea was novel, of course, and agreed. But my intention was always for you to receive hers when she inevitably passed out."

"Why do I need a tin foil reindeer hat, exactly?" John asked, sounding unimpressed.

"I've thought about this for a while now; how he would ensure that every inhabitant in the house was sleeping. It was only when he had me go hunting for stolen government plans for a weapon that scrambles brain signals and causes temporary unconsciousness that I realized how he must do it, and how to counter it."

"So, what, the tinfoil hats keep us from getting our brain signals scrambled and us put to sleep?"

Sherlock nodded seriously. "I need you here so that we can both ensure the other stays awake the whole night, or at least, until Mycroft shows up."

"If he shows up," John corrected sarcastically. "Which is unlikely." Nevertheless, he made no further effort to go upstairs to his own room. Sherlock crept over to where Harry lay snoring softly on the sofa and plucked it off her head, giving it to John. "I look ridiculous." he muttered, putting it on.

"Don't worry, John. It will be worth it in the end."

"Sure it will..."

"Alright, now shut up and hide behind the sofa with me."

"I can't believe I'm actually-"

"Ssh! Can you hear that?"

Sherlock pulled John down to the carpet with him as the fire in the fireplace suddenly died.

"What-?"

"Hooves." Sherlock whispered. "Thirty six, by the sound of it. On the roof."

"You've got to be kidding me."

"Ssh!"

The whole flat was silent for a while. Then there were footsteps from above, a faint rumbling from the vicinity of the fireplace, and then more footsteps. This time, inside the flat. Sherlock gripped John's arm tightly. All of a sudden, a familiar voice could be heard.

"Hello, Sherlock. You've really outdone yourself this year."

John swore under his breath as Sherlock leapt out from behind the couch. "A ha! I knew it!"

John slowly stood up. When he did, it was to a most peculiar sight.

The man standing by the fireplace facing them wearing a most jolly expression was unmistakeably Mycroft. However, he had, as Sherlock said, put on copious amounts of weight, grown a full and rather magnificent beard, traded his customary black designer suits for a traditional red and white one, and replaced his ever present umbrella for a large sack that John could only assume was filled with toys for the good little girls and boys.

"Mycroft... you really are Father Christmas?"

Mycroft smiled. "Of course. I was thought to be the best candidate for the job. I've held far more prestigious positions than this, though."

John choked out a laugh. "What, like the tooth fairy?"

"No, no, John. Of course not. That's Tanya's job."

"Tanya?"

"Yes. She should be along shortly." Mycroft said.

Sure enough, a second later, the rumbling came from the chimney again, and Not Anthea stepped out, dressed in a ridiculous sparkling dress, still texting someone on her Blackberry.

"Little Nellie Wilson in Bristol's lost her front teeth fifteen minutes ago, Mr Holmes. Can we make a quick stop?"

"Of course, Tanya."

"She's Tanya now, is she." John murmered, in a why-do-I-even-bother tone of voice.

Sherlock, of course, soon joined in the surreality of the situation.

"Well, Mycroft," he said smugly. "Now I finally know your deep, dark secret. How does it feel to be caught by your little brother?"

Mycroft shot a smile at Sherlock that was almost sympathetic. "Oh Sherlock." he sighed, "You've been finding me out every year since you were seventeen. Same thought process, same tin foil hat - although, I must say I like the festive motif this year-"

"Harry's idea."

"Hmm?"

"Never mind." Sherlock said. "But that can't be right. I've suspected something was up since I was seventeen, but I've merely been observing you, gathering data since then."

Mycroft shook his head again. "Quite the contrary, brother mine. You've always been up waititng for me, every year since I got the job. Letting you have the fun of solving the mystery has always been my Christmas gift to you. Unfortunately, because this information is top secret, I've also had to wipe your memory every year, but the sacrifife is necessary, and it is so amusing to watch you start fresh every fall."

Sherlock looked quite indignant. "You can't just wipe my memory whenever you feel like it."

"But I can. And I do. And you never know. That's the beauty of it." Mycroft said, smiling serenely.

"Hold on..." interrupted John. "Does that mean you're going to wipe my memory, too? And Harry's?"

"Unfortunately, you are a necessary precaution. Your sister, however, seems quite dead to the world, so there's no point in wiping her too."

"And you won't erase... too much? My IQ will still be the same tomorrow, I mean?"

"Oh, yes. We have tons of experience wiping memories." Anthea/Tanya/Tooth Fairy said without looking up from her Blackberry.

"I don't even want to know..."

Meanwhile, Sherlock was looking pouty and dejected at the fact that Mycroft was continually taking this information from him. Mycroft was assuring him that it was for the greater good, and that if he cooperated he wouldn't tell their Mummy about something about stolen art. Eventually, Sherlock agreed to the mind wipe.

Anthea/Tanya/Tooth Fairy stepped up to him wordlessly and held her Blackberry up to his forehead. A blue light enveloped his head and then he slumped down, unconscious. John moved to help him, but Mycroft held up a reassuring hand.

"He's fine." he said. "We will move you both to your rooms when the wipe is complete. You will wake up tomorrow with no recollection of these events. It's quite painless. Are you ready?"

"Mycroft, you're Santa Clause. There's nothing I'd more willingly forget."

Anthea/Tanya/Tooth Fairy stepped towards him brandishing the Blackberry.

"Wait!" John said before she touched it to his head. "Since I'm not going to know tomorrow morning, can you just tell me one thing?"

"What?" she said.

"What's your real name? I mean, really."

Anthea/Tanya/Tooth Fairy looked at him for a moment, before gravely saying, "Slartibartfast."

Then the Blackberry touched his forehead and the world went black.

"Merry Christmas, Johnny! Wake up, sleepy head!" A familiar voice crowed as a pillow hit his head.

"Ugh... can you tone it down a little, please? You're thirty six, Harry. Thirty six."

"Never too old for Christmas joy, Johnny!"

He tried to bury his head under his pillow, but his siser just snatched it away.

"I had a crazy dream last night." she said eagerly.

"Oh, do tell..." John said unenthusiastically.

"I was there, and you were there, and Sherlock, and some other people too. And we had these wicked reindeer hats, and one guy was Santa and there was this hot girl with him who was the Tooth Fairy and-"

"Harry, please shut up. That's complete nonsense. You had too much to drink, that's all."

Later on, however, when he went downstairs, he found a neatly wrapped parcel containing a new jumper, and a note that said See you next year. -SC

Okay, yeah, it's random and crack, but when the plot bunny nibbles, I've got to let it out. Cookies to anyone who got the Hitchhiker reference. Leave a review, flames will be used to roast marshmallows. Forgive this nonsensical crack! Happy Holidays!