Sherlock suddenly jumped up from the couch, where he had been lying for hours poking at John's laptop. "John, we're going out," he called, and sprinted for his room.

"Where?"

"Club."

John put down his book and headed up the stairs. This was for the case, then - Sherlock despised nightclubs on principle, both for the volume of the music and (in his words) the "concentration of stupid in the air." John's wardrobe wasn't particularly conducive to the current clubbing set - not to mention he was twice the age of some of the regulars - but he managed to dig out a pair of tan trousers and a navy button-down which was slightly too small but at least wouldn't pop any buttons when he moved. Christ, this is pathetic. He wasn't going to look twenty, no matter what he wore. Sherlock was a chameleon, could morph into any disguise, but John was just going to look like someone's frumpy uncle no matter what . . .

"No no no, that won't do at all," Sherlock's voice said from the doorway. "Here, wear this." John turned - and gaped.

Sherlock was poured into the tightest pair of black leather pants John had ever seen. His top half was - John hesitated to use the word "covered" - by a sparkly black fishnet contraption which only highlighted the paleness of his bare skin underneath and the darker spots of his nipples. He had a gigantic sparkly earring dangling from one ear and an assortment of costume jewelry around his neck. And he was holding out a black leather collar.

"Sherlock - what sort of club is this, exactly?" John choked out.

"It's called 'Restraint' - it's a sex club catering to the BDSM community. It took me all evening to verify the connection, but all three victims were members there. That's the where they met the killer."

John blinked. "And you want me to wear a collar."

"It's traditional. We'll go in as a couple - as my submissive, you won't be expected to initiate any sexual activity, and your presence will give me an excuse to look around and talk to people without being expected to participate in anything."

"It won't work."

Sherlock frowned. "Of course it will work. Is it the idea of it being a sex club that bothers you?"

"No." John huffed out a bit of a laugh and raked his fingers through his hair. "They'll never buy that I'm collared. Everyone there knows me as a dom, and I don't switch."

Now it was Sherlock's turn to gape.

John turned back to his closet and dug through to the back, where he kept his fetish gear and outfits. "Not something we've ever particularly had a reason to discuss, I admit. Kinda surprised you didn't know it already, actually - I assumed you'd have ignored reasonable boundaries between flatmates and gone rooting through my stash of toys." He found what he was looking for and dragged the duffel bag out into the room. "So yeah. For what it's worth, I didn't recognize any of the victims, so they weren't long-term members. But if you want us to go undercover as a gay couple, you're going to have to be the one to wear the collar."

Sherlock was still gaping.

John sighed. "Look. Do still want to do this? Because I'm willing, if you think it will help the case. But we're going to have to talk through some things first."

"You've been there before," Sherlock repeated.

John dropped the bag and crossed over to stand directly in front of him. "I used to go pretty regularly when I was younger. Then I stopped in whenever I was on leave." His throat tightened. "I was in a pretty bad place when I was invalidated out, was convinced I'd never interest anyone else again, but Cindy - the blonde I was dating right after I moved in here? - was keen on trying it so we started going back. And I've been going sporadically ever since." He held up the handful of clothes he'd dug out. "Now, if you want me to change, turn around."

Sherlock obediently rotated a hundred and eighty degrees, fixing his eyes on the doorframe. "So . . . you're into . . . bondage and whipping and all that?"

John quickly shucked the his clothes and pulled on the tight silk t-shirt and fitted jeans. He debated, but skipped wearing pants. Everything was black, except for the red leather lightning bolt leading from his right knee up to his hip. "Okay, you can turn back around. Yes, I'm into 'all that.' Let me find my boots, and then we can go downstairs and talk about this."

They relocated to the living room. John calmly worked his feet into his black combat boots, while Sherlock still was obviously having issues sorting everything out.

"If people there recognize you, will they think it odd you're coming in with a man?" he finally asked.

"Not particularly." John flashed him a tight smile. "I haven't brought any men in a while, but I play with both genders - any gender, really, if you want to be pedantic about it. I generally skew towards straight, but it's definitely not one hundred percent."

Sherlock nodded and looked away.

"Right then." John stood, clomped over to stand directly in front of Sherlock, and held his hand out for the collar which Sherlock was still twirling nervously. "Will you wear this collar for me tonight?"

Sherlock brought his head up, then, meeting John's eyes. He looked completely lost. "This isn't how I thought it would go," he said quietly.

"And yet you thought we could swan into a sex club and blend in."

Sherlock licked his lips and looked back down.

"I see." John plopped down on the sofa next to him. "Serious talk time. Are you gay?"

Sherlock hesitated, then nodded slightly.

"Have you ever had sex?"

Sherlock shrugged. "Define sex."

"Orgasm in the presence of another person."

"Then yes."

"Ever suck a cock or have your cock sucked?"

"Yes."

"Ever had your dick inside someone, or had someone inside you?"

"No."

"Ever been to a club like this?"

". . . No."

"Okay." John cocked his head to one side, studying his flatmate. "What exactly did you expect would happen tonight? If I had been willing to pretend to be your sub?"

Sherlock shrugged again. "I expected we'd play a new couple in town, checking out the scene. The victims were all men in their early thirties, relatively fit, professionally-successful types but in fields they weren't likely to have a lot of creative autonomy. From what I've gathered from their friends and families, their personalities would all indicate they'd be submissives in an environment like this. I suspect the killer picked them up at the club, convinced them to go elsewhere for sex, and murdered them while they were consensually incapacitated."

"And you'd recognize the killer on sight?"

"I -" Sherlock made a frustrated gesture. "No way to know, of course, but it doesn't hurt to look. I was planning to start up some conversations with other doms and see who was actively looking for a sub - and who was offering to play with people outside the club."

"I see." And he did. Sherlock would have used him as bait, he would have gotten silently furious, and they would have had a big row about it once they got back to the flat. "This will work better, actually."

Sherlock blinked. "How?"

"You're the bait." John eyed Sherlock's outfit. "I'm just being realistic - I'm half a decade older than you are, I'm five foot six, and I'm not all that much to look at. We'll have much better luck if it sounds like you are the one on offer. You're good at flirting, when it suits your purposes."

"Don't sell yourself short, John." Sherlock blatantly eyed him right back.

"Oh, I know." John smirked at him. "I have the whole military thing going for me. My better qualities mostly come out when I'm ordering someone around, though - I'm not exactly submissive material. Think you can fake it for the night?"

"I -" Sherlock's Adam's apple bobbed sharply. "Might be harder putting myself in position to have the right conversations, this way."

"Don't worry about that." John deliberately dropped his hand to Sherlock's knee and squeezed it.

Sherlock jumped.

"We're going to have to work on that, you know." John kept his hand perfectly still, just a warm weight on Sherlock's leg. "I'm going to have to touch you, and you'll have to trust me to get you into the right places to gather information. Without arguing with me. Do you want to decide on a safe word first?"

Sherlock's forehead wrinkled. "Why?"

"Because if we have one, I won't have to constantly stop and ask for your consent before we do anything new. And I suspect there will be a lot of 'new' tonight. I'll trust you to tell me if something is making you uncomfortable."

"Are you . . ." Sherlock frowned. "You anticipate actual physical contact will be necessary?"

John let out a long breath. "Yeah, honestly," he admitted. "We'll really stick out - you'll really stick out - if you jump every time someone touches you. I mean, it's horribly rude to just go up and manhandle someone just because they're dressed as a sub, but it happens sometimes. And part of the point of playing in a public place like Restraint is all the little incidental contact with other people. Not sexual, necessarily, but the possibility is always there. So if you're not comfortable with the idea of being touched -"

Sherlock grumbled and shifted in his seat. "It's not that I can't stand being touched," he said grumpily. "I just don't like the idea of being pawed at by anyone except you."

That was . . . informative. And unexpected. Sherlock hadn't actually said he wanted John to touch him, but he might as well have. "You're okay with me pawing at you?"

He shrugged awkwardly. "It's acceptable."

"Okay." John nodded. And then tried to figure out how to ask about the elephant in the room. "So, ah, when you say it's acceptable -"

"Anything I've done before," Sherlock replied, cutting right to the heart of the matter. "I acknowledge that some form of sexual play may be necessary, and I'll tell you if you've hit my limits." He looked away and swallowed. "I suppose I'll have to . . . follow your lead in that arena."

"Right then. Pick a word?"

Sherlock hmmmed. "Red-yellow-green is traditional, I understand. And if I tell you I'm thirsty, that's a cue for us to get somewhere quiet and either regroup or leave."

Right. I can work with that. "This is going to be one of the stranger things we've done together. Just so you know."

A tiny smile flitted around Sherlock's lips. "I know." He held out the collar and raised an eyebrow.

John stood, took the collar, and clasped it neatly around Sherlock's pale neck. It looked . . . very good on him. He grabbed his duffel, offered Sherlock a hand up, and didn't release his grip until they got into the cab.