They invented the game by accident.

Sherlock was bored. And it was a bad one. John had tried everything, but every trick he'd picked up so far (and there were quite a few) went nowhere. Sherlock went from bad to worse. After he broke a window, causing Mrs. Hudson to run upstairs in alarm, and he was horribly, inexcusably rude to her, John just lost it. Like all of their rows this one was loud, viciously honest, and brief. Then they each disappeared into their own bedrooms.

When Sherlock emerged an hour later, shivering in the icy wind blowing through the broken window, he wasn't surprised to find John had left. He'd gone out to cool off, he'd be back by midnight, probably bringing some plastic to cover the window. No, it was too late, the stores would be closed. John would have to take care of it tomorrow. So Sherlock made a fire, wrapped himself in a duvet, and sulked. He was still cold, though, and since he didn't own a jumper he put on one of John's. It smelled like him. John should be at home, he thought. He should be here, irritating me with his little brain, setting my teeth on edge with his normalcy, infuriating me with his rules and his order, being John.

He curled up in the jumper, on the floor in front of the fire, and sent a volley of texts, all carefully designed to capture John's attention, but received only one response:

Stop.

He gnawed thoughtfully on a fingernail, considering his next move. If John didn't want him to text, he decided, there was only one thing for it. He stood, slithered out of the jumper, and leaped elegantly across the Corbusier. Shoes, coat, scarf, gloves, and he was bounding down the stairs and out the door. The angle of the doormat told him John had headed west.

He tried all the pubs John liked and the ones that he didn't yet but would if he knew about them. He checked the parks where John enjoyed a stroll as well as the dark alleys and rooftops that Sherlock preferred. He texted Harry, Clara, and Sarah, and was told to bugger off, piss off, and sod off, respectively.

Lestrade: I know nothing, keep me out of this.

Stamford: Haven't seen him in weeks, mate. How've you been?

Mycroft (unsolicited): Trouble in paradise, brother? May I be of assistance?

The last one he promptly deleted as he returned to his investigation. As usual, human informants were useless. But this pub, this was the one. A chair turned away from a table just-so told him everything he needed to know as soon as he walked through the door, but the bartender confirmed, John had just left. It was a good distance away from Baker Street. With his bad leg, John would be moving slower now. Exiting this pub, he would have walked downhill, southbound. Several blocks down the street, almost out of sight, a CCTV camera had just finished swiveling, following something that continued around the corner, to the east. Sherlock walked faster, peeling off to the left just before that corner, taking a shortcut through the alley.

John wasn't really angry anymore, just bone tired, exactly as he wanted to be. He'd loop around this block and then start heading back to Baker Street. It would be cold there – Sherlock would have done nothing to cover the hole in the window – but it would be warm enough in his bedroom, where he'd sleep alone. When he got in these moods Sherlock didn't want to be within arm's reach of him. Just wanted him around. Tomorrow, John would buy plastic sheeting to cover the window and march Sherlock downstairs with an apology and a cheque for Mrs. Hudson. Tomorrow, maybe, please God please, there would be a case. Tomorrow, because he lived with Sherlock Holmes, John knew anything could happen. Tonight, a hot cuppa, a couple of paracetomol, and a soft bed were all he asked. Also, he prayed Sherlock wouldn't be torturing his violin. (In the back of his mind he prayed Sherlock wouldn't have sank deep enough into his boredom to be doing something worse to himself, but he didn't let himself think that consciously.) He rolled the tension out of his bad shoulder and strode down to the end of the block.

Out of nowhere, a hand shot out of the shadows and grabbed his right wrist. John didn't think, just reacted with a left hook, but the figure dodged and grabbed that wrist as well, pinning both to his sides, and by that time John already knew, and was smiling in spite of himself. I should be angry, he told himself. In a healthy relationship, people don't… But he didn't even try to complete the sentence. Instead, all he could think was: Here's Sherlock, not being bored, not in the least.

He beamed as Sherlock smirked with delight and said, "Got you."

"Yeah," John breathed. "Yeah, you certainly have."

.

The rules of the game were as follows:

1. It had to be random and it had to be infrequent.

If John disappeared every time Sherlock got bored, or every time he reached a certain level of arseheadedness, the game would necessarily become boring. So John was very careful to avoid any kind of pattern. He might go several months without attempting it, then he might go three times in a row. He might do it once at the first sign of boredom and on another occasion wait until poor Mrs. Hudson was at her wits' end. But he couldn't, unfortunately, do it every time she was that upset. He loved Mrs. Hudson. But not as much as he loved Sherlock.

2. John had to have a head start.

He'd never attempt the game if there were any chance that he'd been seen leaving the flat. Sherlock quickly caught onto this rule and, without ever discussing it, withdrew into his bedroom more frequently during his moods, giving John ample opportunity to disappear. But referring back to the first rule, John rarely took advantage of those chances. Many times Sherlock flew out onto Baker Street to look for him only to discover that he'd just ran down to the Tesco for milk, or was having a dull dinner with Harry. On those occasions, Sherlock's mood plummeted even further. That was the cost of admission for the game; a high price, but worth it.

3. Every treasure hunt must have its treasure.

For Sherlock, the prize was John. For John, the prize was at home. They'd take a cab back to Baker Street in silence, both relishing the end of boredom, the peace – however temporary – enveloping them, and the hum of anticipation. Once inside, Sherlock would strip John, slowly, murmuring his methods into John's skin.

"A homeless woman saw you walking on Mepham Street," he'd say, dragging his lips along John's neck.

"You had to go to the pension office this morning, I knew you would have started from there," he'd explain, flicking his tongue across John's nipple.

"I smelled you in the library," he'd whisper against John's hipbone.

"Your fingerprint on the railing," he'd breathe into John's thigh.

John wouldn't argue, would never say Sherlock, you can't possibly have seen my fingerprint, he would just close his eyes and listen. The longer the hunt, the greater the challenge, the more decadent his reward. And when they were exhausted and spent, John would run his fingers through Sherlock's hair and say, "You're amazing," referring to everything, all of it, and Sherlock would hum in reply.

.

It didn't work always work out as well as they both might have liked.

For example, there was the time John had the flu and – being a skilled and experienced physician – didn't even notice.

He'd had an elaborate plan that evening. For months, he'd been stockpiling ideas, waiting until he had a reason to put them all together into one intricate escape route. When the time came and Sherlock was clawing at the ceiling, John slipped away. But the temperature dropped suddenly and he wasn't wearing a proper coat. And, since he'd had to wait for Sherlock to hide in his bedroom, he'd left the flat quite late. So by the time he realized how very cold and tired and possibly miserable he was, there was no nice warm pub or coffeeshop for him to take refuge in. He briefly considered aborting the mission, texting Sherlock and telling him to meet up back home. But no. That would break something. It wouldn't be right. Nights in Afghanistan were colder than this, he told himself sternly. They weren't so bloody damp, though, he grumbled in reply. He was a Londoner through and through, but not by choice. If anyone had asked him his preference, he would've been born and raised in the Mediterranean or southern China or bloody Las Vegas. Anywhere warm and preferably dry.

"Got you," Sherlock called smugly as he walked towards John, hunched over on a park bench. But before "you" had left his lips, he had taken in all the information, so it went from smug to angry in a single syllable and actually came out, "Got you are sick John you idiot you've got a fever we're going home right now." In the cab, John insisted he was fine, just tired and perhaps feeling a bit poorly, but anyway cold weather doesn't really make you sick, that's just a myth. And Sherlock replied no of course not, but it will break you down if you've already got a virus and look at you, your breathing sounds horrible and you're shivering like mad, come here you bloody moron.

Back on Baker Street, John took a hot bath and curled up in bed with tea and honey under Sherlock's disapproving glare. But rules are rules. Sherlock was no longer bored and that meant John was owed a reward. He trailed his explanations and deductions across John's arms and ribs, wrapped them in kisses and placed them carefully on his stomach and legs, and then – ignoring the wheezing and sniffling and occasional cough above his head – gently took John into his mouth and put him very sweetly to bed.

.

Once John had the brilliant idea of tricking Sherlock into taking a holiday.

The game had never taken them out of the city before, and he was a bit nervous about it. Would a two-hour train ride to Cardiff intrigue Sherlock or irritate him? It would be unexpected, he decided, and that made it worth the risk. So after a complicated route through the city, he boarded the train and hoped for the best.

He was feeling hopeful as he walked from the train station to the hotel, until he checked in and was told, "Ah, Dr. Watson. Mr. Holmes is expecting you, he's already upstairs."

Sherlock – reclining on the bed with wet, rumpled hair, wearing only a bathrobe, sipping a glass of wine – appeared to have been there for some time. He looked up from his mobile and smiled. "Got you," he said pleasantly.

"How'd you know?" John asked, crestfallen.

"You forgot to clear your search history."

John groaned and dragged his hand across his face.

"I still had to figure out which hotel you'd choose," Sherlock volunteered.

John narrowed his eyes suspiciously. He'd mucked it all up and Sherlock ought to still be bored and furious with the world. Cranky, at the very least.

"Besides," Sherlock continued cheerfully, turning his attention back to his phone, "they've just had a body wash up on the shore this morning. It's all over the papers. Lestrade's working on getting me access with the local imbeciles. Let's have sex now, and by the time we're finished we'll have something interesting to do."

.

Then there was the time John couldn't get himself found fast enough.

He really threw himself into the game that night, intentionally planting clues to lead Sherlock astray, doubling back and circling round, really (he thought) doing the best he'd ever done. He was so absorbed with the signs he was leaving for Sherlock he didn't pick up on the signs all around him. Like the two men who'd been following him ever since Brixton Station. He'd already walked to the other side of the bridge and then retraced his steps, hoping Sherlock would continue following the false path on the other side. Then he skittered down a concrete slope to cross underneath the bridge, raised up both hands to balance himself on a concrete pillar, and felt something hard push between his ribs and an even harder voice grunting, "That's perfect, Watson. Don't move a muscle." Another pair of hands was already patting him down and removing the gun and mobile from his pockets.

The two men started marching John back up the bank, walking just behind him on either side, close enough to keep the gun in near-constant contact with his back, just far enough that he could never quite see their faces, muttering instructions as they went. He was silent, obedient, and extremely clumsy. He dragged his feet, hoping to leave traces of shoe rubber behind on the concrete. He staggered awkwardly, planting footprints in patches of dirt and grass and rubbish. He stumbled, throwing out his arm to catch himself on a wall and leaving fibers from the cuff of his jacket clinging to the bricks. He pretended to be stupid with fear, but his mind was clear and sharp, remembering every clue Sherlock had ever recited onto his body. He tried to use them all. With each step, he left a note that said: It's me. Follow. Hurry. He wished he also knew how to say: Bring help. For God's sake, be careful.

They entered a storefront, a travel agency, John tripping on the welcome mat to leave it askew, and passed through the office to the storage room behind. There, they duct-taped his hands, feet, and mouth, and left him in the dark.

Olly olly oxen free, John thought grimly. Come on, Sherlock. Time's up. He squirmed patiently, persistently, but he knew it was useless. The last time he was kidnapped, they'd been dumb enough to use rope and he'd already slipped out of his bonds and kneecapped his captors by the time Sherlock showed up. John remembered how Sherlock's eyes had widened, then narrowed, then darkened as he took the scene in, and what would you call the look in his eyes then, and all the way home in the cab? In anyone else you'd call it hunger, but John had never seen Sherlock look at food like that, not even close. Desire didn't begin to describe it. It was the edge of a vast, black chasm, it was terrifying in the best possible way. He remembered how Sherlock had thrown him up against the wall the moment they got home, the heat of his breath and rumble of his voice as he growled "you… are dangerous," and dropped to his knees. At that moment John had caught himself thinking, in all seriousness, "I really should shoot people more often."

He liked to think Sherlock brought out the best in him, but if he was being honest he knew that wasn't strictly true. At all.

And anyway, he couldn't shoot anyone now, rendered helpless by polyester, fiberglass, and polyethylene on a cold cement floor.

He spent his time working through a number of scenarios, figuring out how to take advantage of any hint of an opportunity. His approach was an inspired combination of PTSD, military training, and "what would Sherlock do." It had served him well before. But it was useless when there was nothing to work with. Time stretched on, and John's state of mind fluctuated across irritation, anxiety, panic, resignation, and rage, in every possible order.

And then finally, finally, finally. A thud. A crack. An almost-shout, suddenly cut off. Footsteps, running – just one pair, the bastard came alone – and a door flinging open, flooding light into the room. A tall dark figure swooping down with a coat billowing like wings, long cold fingers grasping John's face, then tracing down his bones, looking for damage, and eyes like blue flame searching for any sign that John's health was less than perfect. All this in seconds. And then, satisfied, Sherlock grabbed the duct tape across John's mouth and Jesus-motherfucking-Christ-shitshitshit-that-bloody-HURT, Sherlock! But it was ok, there were soft, angelic lips pressing everywhere the tape had been, and a tongue lapping at his face, which was weird, probably he shouldn't have liked it, but it was heavenly actually, soothing his burning skin, and John opened his mouth and fell into the kiss, grateful and smug. They'd won again; evaded death one more day.

Sherlock swiftly cut through the duct tape at John's wrists and ankles with his pocket knife and pulled him to his feet. A siren wailed in the distance, coming closer. Gold and green sparked through the blue of Sherlock's eyes as he stared at John with a searing intensity and gripped his shoulders tight.

"Got you," he whispered.

.

And sometimes, it was just perfect.

There was the time John finished his shift at the surgery and slipped out the back so that no one would see him leave. He decided on a straightforward approach that afternoon; none of the convoluted mazes he usually traced through the city. Instead, his cover would be other people.

He bounced from one crowd to another. The shopping hordes of Camden and Covent Garden. The tourist mobs of Westminster and Greenwich. The pinstriped and double-breasted throngs of the Square Mile and Canary Wharf. It was a sunny, unusually warm day in early spring and the people of London were cooperating beautifully with John's plan.

As rush hour set in, he disappeared into the Tube, switching lines constantly, transferring at every major junction, almost two hours pressed among the commuting multitudes.

And then, on the eastbound Hammersmith & City Line, suddenly he knew Sherlock was there.

Just before they made contact he felt that familiar heat behind him and leaned back slightly as if to say yes, love, you win. Sherlock reached up to grab hold of a strap and took the smallest step forward so that his body just brushed up against John's. Both men were silent, their breath deep and even and perfectly matched. When the Tube lurched, Sherlock stumbled forward, colliding into John, his free hand glancing across the other man's waist, fingers barely lingering on his hip. When more commuters boarded, jostling each other closer together, Sherlock appeared irritated but calmly, steadily, pressed his body against the one in front of him. Every bump and twist in the Tube's path was a reason for John to rock back on his heels and rub against the warm body behind him, to turn his head a bit to the left so he could feel hot breath and soft lips against his face for just a moment.

The ride felt like hours. At last they arrived at Baker Street and stepped off the Tube. Without a glance at each other, both men carefully wrapped their coats around their bodies and strode purposefully up the stairs to the street. Anyone walking alongside them would have been surprised to see them enter the same flat. Such a person would have been shocked to see what they did inside.

To wit: Sherlock whipping John around to push him, face-first, against the door he had just closed and grinding against him; John arching his back and reaching behind him to grab Sherlock's arse and pull him tighter; Sherlock reaching around to grab John tightly through his trousers and John groaning wordlessly in response.

Then Sherlock pressed his lips against John's ear and rumbled, "Got you."

And John exhaled slowly and said, "Go on, then. Tell me how."