John liked Lestrade's crew. He was comfortable around them, for one thing; police and soldiers lived in similar worlds in some respects. For another, they really knew how to throw a holiday party. The eggnog was homemade, the music was live, courtesy of the CID's very own barbershop quartet, he didn't think it was his imagination that the girls from Intake were plotting to catch him under the mistletoe, and this was the first chance he'd had to dance since the case of the disappearing night club logos.

After a couple of turns about the floor with Sally, who turned out to be an excellent dancer, he headed back to Sherlock, whom he'd caught spectating with a wide, amused grin. "She had better not become the next Future Ex-Mrs. Watson, John, or you and I are going to have to revisit the terms of our arrangement."

John sneered companionably at him, but his unutterably witty comeback was lost to posterity beneath Dimmock's shouting from the door. "Hey! Hey, you lot, I've got an arrest to book. While you were up here getting soused, I caught this bloke trying to creep down the chimney into the boiler room." A general uproar ensued as he led Lestrade through the door in a baggy Santa suit and fake handcuffs in the face of much hooting, hollering and catcalls.

John joined in the laughter and applause. It was only by dint of being so keyed in to all things Sherlock that he spotted the wet-cat bristle before Sherlock turned his back on the whole affair.

"Sherlock?"

"I'm going to get more sangria," Sherlock pronounced in the grim tones of a man going into battle. John watched him head off to the other room, baffled, then shrugged and turned back to the show. Honestly, the man's ego got ruffled over the strangest things.

It happened again three days later. They were at Canary Wharf when Sherlock hissed and changed direction mid-stride. Used to this sort of thing, John followed automatically, on the alert for any shadowy figure or suspicious character that could've provoked the sudden detour.

He saw Santa Claus, an infinite line of kids, and their orbital belt of parents.

Maybe it was one of the parents? John had to admit it wasn't his first instinct. No one looked suspicious when they were toting children.

But one look at Sherlock's frozen, Santa-avoidant expression said otherwise.

"My god," John blurted, "who's in that costume?" The only people capable of putting that look on his face were Moriarty and Mycroft. Granted they were both exceptionally clever men, but John was fairly certain neither of them were lurking under that luxuriant white beard.

But he had no time to muse over it. His flatmate stretched his legs to their full extent and belted off out of Jubilee Place as fast as he could go without running. John had to jog to catch up.

John said nothing on the walk out to the street, or during the cab ride, but he had learned the hard way that when Sherlock reacted that extravagantly, he needed to know why. Once they got home, where the logistics of escape grew complicated, he rounded on Sherlock. "Who was in the suit?"

"What?"

"Who was in the Santa suit? Sherlock, that was your 'we're about to die and not in a fun way' face."

Sherlock hurled his coat to the sofa. "I have no idea who was in the suit, John."

That was his 'why are you wasting my time with irrelevancies' voice. John frowned, recognizing that he'd somehow got hold of the wrong question. "Then why were you running away from him?"

"I wasn't running!" And then Sherlock did it again, spinning to make a beeline for the nearest door.

It was the kitchen. John followed him. "Sherlock! What about a perfectly innocuous children's park Santa could put you in this state? Did the man have a bomb in his sack? Were there sniper elves? Was he part of a crime syndicate or working for your brother or something?"

Sherlock braced his hands on the table and glared up at John, generous lips pressed thin and white. "iNow/i you decide to practice your deductive skills. It had nothing to do with the man in the suit, John. Leave it!"

John studied him carefully, assessing whether he had any chance of getting further if he pushed. "Alright," he finally conceded. Fine. If Sherlock wouldn't tell him, John would just ask someone else. He was done with being kept out of the potentially deadly loop.

Lunch with Mycroft was a rare but always interesting event. He knew the most unusual restaurants in London. John would never have taken a bet that he'd willingly walk into a vegan café, but this was really quite good.

"One look and his face went white," he said over his seitan makhani, "and the next I knew we were dodging behind the reindeer. I couldn't get word one out of him after."

Mycroft delicately dabbed crumbs off his mouth. "I really had expected him to be over this by now."

"Over what?" Oh god, they were all going to do that thing where they talked in code, weren't they.

Mycroft peered at him in a distinctly ithoughtful/i way that made John's paranoia sit up and roll over. "I suggest you check the chimney flue at your flat, John."

And that was all he'd say on the matter.

John fumed on the way home. God knew what he was meant to find in the chimney flue. Undoubtedly the traces of ash left behind by the burning of a slightly different-colored paper than they normally used would be a dead giveaway to the whole puzzle. Assuming John had a giant brain that could tell such things.

He checked it anyway when he got back. Wasn't like he had anything else to go on.

When he ducked down to look up into the chimney, he nearly had his nose taken off by a mantrap.

Half an hour later he snapped, "Sherlock!" the instant his flatmate cleared their sitting room door. "Why are you trying to kill Santa Claus?"

Sherlock froze.

John pointed accusingly at the fireplace. "If I'd put my arm in there to check the dampener, I would've lost it! Look, it's your own business if you want to trap and experiment on fictional creatures, but leave the flat out of it!"

Sherlock's body stuttered. "…Experiment on fictional…?"

John felt his jaw bruise as it banged off the floor. Oh god. "You…you do know Santa isn't real. Right?" Please. Oh please. John couldn't handle a world in which Sherlock 'Logic is my only God' Holmes still believed in Santa Claus.

A slow blink. "Technically, he was real. Saint Nicholas served as Bishop of Myra in the fourth century-"

"Yes, yes, never mind!" John's hands paused mid-waveoff. "Wait. Why do you know that? You don't pay attention to astronomy; what do you care about the lives of saints?"

Sherlock's body lost structural integrity, crumpling into John's favourite chair. "That bastard plagued my childhood," he spat.

A profound calm stole over John as gravity inverted in his head. "Come again?"

Sherlock growled and snatched at his hair. "It's complete rubbish! Everything about him! He haunted me from the age of two. Every adult I encountered persisted in attempting to convince me of the reality of this phantasm that could defy the laws of physics to stalk, spy upon, and award children who fell under his arbitrary favour with mind-numbing playthings."

There was no way to reply to that. It wasn't really a question, anyway, but John…well, yes, alright, the whole 'sees you when you're sleeping, knows when you're awake' thing had occurred to him as rather stalkery, but then he'd always had a morbid imagination.

"He creeps down the chimney, John," Sherlock was seething. "No one has ever seen him. He comes and goes and eats all the cookies and possibly your parents lie safely abed upstairs while a total stranger moves unimpeded about your house ior/i they might actively abet him in this insanity! This is what they try to persuade you of! Can you understand what that does to a child's mind? To have adults heaping lie upon terrifying, implausible lie on you while it says right there in a book that the man himself served as a perfectly respectable clergyman and died in ancient Rome nearly two thousand years ago?"

"I. Well." John tried to gather his thoughts. Of the positive millions of adults who had once been children who believed in Santa Claus, he thought he could safely claim that an extreme minority of them, at most, had found it psychologically damaging. "To your mind, yes, I can…." Oh god, wait. Sherlock's mind. "You tried to observe and deduce him, didn't you."

The lack of answer was an answer in itself. "Do you know where Myra was? In present-day Turkey!" Sherlock threw up his hands. "Why would someone from a Mediterranean climate move to the bloody North Pole? And the elves! I don't even know where they came from! I've spent years researching the elves, John. They're like the Easter Bunny. They come out of nowhere. And the reindeer!"

"Ah, well, you'd need reindeer to move about at the North Pole, wouldn't you?" John said sagely before he thought. He received a look that could peel paint.

"They can fly." If Sherlock had the power to condemn souls, eight—possibly nine—cervids had just been cast to Hell. In the circumstances, bringing up the question of Rudolph's validity in the canon of Father Christmas seemed ill-judged.

The breathtaking loathing for flying reindeer was what jarred John back to the real world. "But you understand none of it is real," he reminded gently.

When Sherlock wrapped his arms around his head with an incoherent snarl, it actually drove John back a step in shock. "I know it's not damn well real!" he roared. "That's the whole point! Everyone knows it's not real! What is wrong with people?"

John held out a hand to him—placating or comforting or restraining or he didn't know what. "It's for fun, Sherlock. It's like a storybook. It's part of the magic…of…" As a soldier, John had been trained to spot death traps. One was staring him down right now, daring him to finish that sentence. "I'll just make us some tea, shall I."

He made the tea silently, allowing Sherlock time to sulk by the fire and calm down a little. Then he came back out to hand Sherlock his mug, and sat down across from him, in Sherlock's favourite chair since Sherlock was still occupying John's.

"So…if you know he's not real, then why bother?"

Sherlock shrugged and muttered something avoidantly into his tea.

The merciful thing might have been to let Sherlock get away with that. The subject clearly made him uncomfortable. But curioisity was eating a pit into John's stomach. "I didn't catch that."

"I said it helps me sleep!" Sherlock snapped, then stuffed his face back into his mug, pulling in on himself to give the impression of an unhappy, tea-swilling vulture.

Sherlock was bracing for mockery. And, well, yes, it was funny. No, alright, it was bloody hilarious, but John was hardly going to make fun of him for having a quirk that actually made him seem like a human being.

Everyone had their way of honouring Christmas traditions. Sherlock's was just…characteristically idiosyncratic.

Besides, if John had ever thought of setting traps for Santa Claus, he would've been doing it since he was eight. He looked at the fireplace, thrust his tongue into his cheek, and nodded. Then he took another few seconds to mentally rub his hands together and chortle before he spoke. "I'm seeing years of wasted opportunity here."

Whatever Sherlock had expected, it hadn't been that. He emerged from his mug with a blank stare. "What?"

John shrugged. "All these years trying to fend off a man who didn't exist, when you could've been at capturing him?" He clucked his tongue. "Honestly, Sherlock, I'm disappointed. Wouldn't it be more effective—more logical if you want to disprove him—to try to trap him?"

Sherlock's head rotated just a tic to one side so that he could observe John with the sidelong caution of someone who suspected he might be talking to a lunatic. "He isn't real, John. You can't capture something that isn't real."

"Yes, and the more times you fail to trap him, the more evidence you've got to make your case with." He pushed up out of his chair, confident that it would only take Sherlock a few moments to wrap his mind around the mad logic of storybook reasoning while John assembled a small plate of milk and biscuits. "And tell me honestly," he called from the kitchen, "which is more fun to say to people? 'Santa Claus isn't real,' or 'I've spent the last ten years attempting to capture him and I have yet to encounter so much as a DNA sample?'"

He came back out and set the plate on their mantel, then turned back to Sherlock with a wide, far-too-amused smile. "There. Trap baited." Oh god, he wanted photos of everyone's faces when he told them about this.

Sherlock's eyes glittered. "Wait." He lunged to his feet to scribble on a sticky note, then walked over to stick it to the plate.

Not for Mycroft.

"There. We wouldn't want to capture the wrong fat man with an implausiblly broad spy network."

John laughed. "You got a lot of coal for Christmas, didn't you."

"I didn't!" Sherlock grinned down at him. "What do you think my first clue was?"

Thus was born the new Christmas tradition of 'Santa Baiting' at 221B.