It wasn't a question of trust.
John Watson had trust issues. He knew it, his therapist knew it, Mycroft Bloody Holmes knew it. Trust came as easily to John Watson as emotions did to sociopaths - it was against his nature, his very being shied away from the prospect. So it was with great surprise to all (and especially himself) that John Watson realised that, having been so thoroughly dissected by the man, he found himself with practically nothing left to hide and therefore no reason to stop himself from trusting Sherlock Holmes. If those eyes had not been quite so piercing, if the younger man's rich baritone had not cut through to his very core quite so cleanly, John might've been able to stop himself. He could have found some small, frivolous reason to withhold himself from the other man and be done with it.
Of course, that hadn't happened. And John was bloody glad for it too.
But not now.
The reason you need to know all of this is so that you can understand perfectly that it most certainly was not a question of trust that made John Watson's sweat turn cold as Sherlock began to loop the scarf quite expertly around his wrists, forcing his arms up towards the bars that formed the headboard of his bed. His confidence in the other man did not waver as desire trickled slowly out of John's eyes, replaced with something hard and desperate and unfathomable. He noted with passing interest how a soft, cashmere scarf could feel so akin to fraying rope, and began to wonder at how the heat of another person's body was so comparable to the crackling, dry heat of the desert. John took a deep, steadying breath, trying so desperately to break through the solid wall in his mind and ignore the voice screaming from atop it, telling him to fight, to break free, run run run.
If it were anyone else, he would've said no. If it were Sarah, or Clara, or some other girl who had caught his eye at any point, he probably would have bolted without a word, stormed off in one of those moods that left the offending party feeling just as lost and alone and angry as the offended did. No, it had to have been Sherlock, eyes dancing with the sort of excitement that normally only an abstruse cryptogram or intricate analysis could draw from him, leading his bewitched doctor up to the bedroom and discarding coat and shirt and shoes along the way. The scarf had stayed. It stayed around his neck when everything else had gone and John was so very hard and Sherlock's brain was beginning to get that somewhat pleasant haze that came with being so close to John and it had all been going so well, really, it had.
The turning point had been so subtle, John almost didn't notice it amongst his moans and Sherlock's whispered facts about whatever part of John's anatomy he had deigned to touch with his ethereal hands at that particular moment in time. Those hands had worked their way across John's shoulders, past the shoulder, across and up, up his biceps and towards his elbows, and John's arms were over his head now and he arched up, desperate to reach, to touch-
It was the grip around his wrist that made him freeze. One hand, nail of the index finger digging into his right pulse point, squeezing them together so hard that the bones ached. A ripple of a dark memory pressed at his vision and he closed his eyes, forcing himself to bury it within the darkness. When he opened them again, Sherlock's collarbone was blocking his vision, and John was so wrapped up in admiring the structuring of the detective that he failed to observe the absence of the scarf, though he had certainly seen it was gone. Then the material was suddenly on his wrists, and Sherlock's murmur of explanation in his ear. The detective didn't question John as to whether it was alright or not, whether he had a problem with it. God how John wished to hear Sherlock's oft-infuriating murmur of "Problem?" John supposed Sherlock simply knew John trusted him, would trust him enough to let him do this, to submit himself in such a manner.
The tremors had started. John began to tug at the bonds slightly, when Sherlock was otherwise occupied with marking his hips with tooth and nail, hoping he could easily slip free and just get back to this moment, but of course, that would be doing discredit to Sherlock's knot tying abilities. Inescapable, naturally. John took a steadying breath and told himself that, really, all he had to do was keep the trembling from reaching Sherlock, to disguise it as pleasure. Christ, it had taken him enough time to convince Sherlock that having sex was a very good idea and that, no, it wouldn't distract him from thinking for too long, and that the moments of release could actually be quite useful when one needed to clear one's mind and focus and yes, of course he could top. He couldn't suddenly declare that this was not okay, that Sherlock had to stop and then watch the man pull the situation to pieces and decide it was his fault John was ready to have a breakdown and declare sex entirely off the table. That was the sort of dramatic thing that Sherlock did, and John couldn't have that, no matter whether or not this was okay.
But it wasn't okay. It really, really wasn't okay, and then it was so much worse than that as he lost visual. It wasn't 'blacking out', per se. No, that would've been preferable. What actually happened was that John tuned into a different channel completely, replacing brunette curls and white skin with darkened shadows hiding in corners, the glint of a muzzle pressed against his throat, and then John's breathing filled his ears as he remembered. Remembered the shadows as they took on human form, screaming demands at him, ripping at his flesh as they did so; the man he was so sure he had been replaced by a void, an empty shell; the stench of piss rousing him from the one fitful slumber he managed to attain, and the lack of shame as he realised it was his own. That was what had frightened him the most, afterwards. The loss of feeling during that time, how he had managed to so successfully close off and take it, every beating, every humiliation they had subjected him to, and yet they had never gotten a rise from him. John had known it would catch up with him, one day. He just wished it hadn't been today, at this moment, next to someone who John could so easily break, tarnishing everything he'd spent so long building up.
Sherlock left his thoughts entirely as their hands were suddenly on him again, reaching towards his bonds and John kicked out, foot connecting with bare skin as he roared, they wouldn't fucking take him, never, he was getting out of here alive. He kicked and kicked, each time his foot finding it's target, barrelling into bare skin without restraint, without mercy, aiming to do as much damage as possible while he still could. In one unexpected movement, his captor all but tore the rope from his wrists, and the bedroom reappeared so quickly John felt as if he had given himself whiplash, and Sherlock was at the foot of the bed, eyes darting over him, and - oh God. One hand clutched at the offending scarf, knuckles even whiter against its rich obsidian, whilst Sherlock's other arm was wrapped around his chest, clutching at reddened skin almost absentmindedly, though John knew Sherlock would kill him for ever using such a hateful adjective against him.
"John." Sherlock's voice was as calm and crisp and clear as the first time they had spoken, and John turned his head away, gasping for breath, trying to give himself time to think of a way to explain himself out of this. 'Yeah, sorry, Sherlock, I thought it would be incredibly sexy if I started having flashbacks to the war and beat the shit out of you in the middle of you sucking me off' didn't really seem to be a viable option. What John really needed right now was a bloody hug, and a sympathetic ear, and a cup of tea. All things Sherlock was inherently incapable of providing. He clenched his fists, wishing he could get up and leave, but damn it, all of the strength was gone from his legs and the walk to his bedroom would feel like walking the fucking Great Wall of China. He couldn't even speak to apologise, to try to start making it right because the moment John opened his mouth he'd start bawling like a child and, though he was very good at turning the waterworks on and off, Sherlock could not handle real, unrestrained grief, and John needed to grieve. So he channelled his tears into silence and let everything else hang in the air, waiting for the moment when Sherlock would get up and leave him in that cold, empty room.
The bed creaked as Sherlock finally moved, and John shakily let out a breath he didn't know he was holding. Sherlock's movements were awkward, and he winced slightly as he stood. John wondered for a brief moment if he might've broken a rib. His legs were a bit on the short side, but packed a mighty powerful kick when the situation required it. He let his thoughts drift from the mundane to the earth-shattering as Sherlock, instead of moving over to the door, fetched a bright orange blanket from the bottom drawer of his wardrobe, and brought it over to the bed. John watched in confusion as the blanket was tucked around his body by the younger man, with Sherlock being extremely careful, John noticed, to press it in at his sides tight enough to stop the cold that had spread across John's body as his sweat cooled, but keep it loose enough that John felt in no way trapped by the plush tangerine material. The detective then lay next to his doctor, the tip of John's shoulder as it peeked out of the blanket pressed against Sherlock's skin. Nothing was said, no looks exchanged or sounds elicited from either of them. John knew that this was more than he could of ever hoped for from Sherlock, and Sherlock understood this and knew that John would understand that there was no need for thanks or apologies. They simply lay there as John cried until there was nothing left in him, by which point the bruises on Sherlock's chest were beginning to swell and purple, and the first light was creeping in through their window. Unceremoniously, Sherlock got out of bed and moved over to his bin. Emptying all of the contents of the metal pail onto the floor, he then placed it at his bedside, the side where John was lying. Sherlock then collected the scarf from where he'd hidden it behind his wardrobe, and threw it in, standing still next to it, obviously waiting for something from John, who was still finding it hard to look at him just yet, all things considered.
Eventually, John knew what was to be done, and he met Sherlock's eyes. Still nothing passed between them, no looks of understanding, unsaid apologies or declarations of love behind their gaze. It was just a connection, the signal for Sherlock to take action. It was one they maintained as Sherlock dropped the match that had been burning his fingers into the bin, and as he came back to John's side on the bed (making sure to walk around rather than clamber over him), and one that they only broke as Sherlock pressed a rare kiss to the top of John's head, before settling down next to him. And there they remained for the rest of the day, Sherlock with his Blackberry at his fingertips, tapping away contentedly, and John slowly trying to tackle the snapshot memories of the worst week of his life, finally allowing himself to encounter those emotions as his entire being was warmed by the presence of the only man in Christendom he trusted, the dying flames of a cashmere scarf, and a fluorescent shock blanket.