The impact to Sherlock's face was a surprise.
He had imagined various possibilities for how John would respond to his intelligent and well-designed return, and yet physical violence was not one of them.
He had expected initial shock, yes, but he imagined it would be followed by a rush of guilt and relief, ending with a display of affection, perhaps even a hug.
Dabbing the blood off his face with a tissue, Sherlock didn't even wince. Of course he had suffered wounds much more grievous than this tiny blemish, but there was something about it that was so much more painful than any mortal wound he had endured.
Thinking of the map of crossed scars that marred his back, and the way they rubbed achingly against the inside of his shirt, Sherlock knew he had never felt more physical pain than he had during his time in the Serbian torture room. Every now and again, even though it had been weeks since his escape, the scars would scab and crack and he would spend several frustrated minutes trying to stem the bleeding, his arms not quite long or flexible enough to reach the wounds on his back. He refused to ask anyone for help, despite knowing that Molly would, without hesitation, willingly bind and bandage his wounds for him.
His reputation meant more to Sherlock than he was willing to admit out loud. Returning to London left him in a position to seem invincible, the man who defied death. He was not going to admit his injuries to anyone.
But when he stood in the bathroom of 221B Baker Street, his bare back to a mirror, as he tried unsuccessfully to change his bandages and slather salves and creams across the broken and bruised flesh of his mottled back, he wished for one brief moment that there was someone who he was unafraid to appear vulnerable too. That he trusted someone enough to share with them his deepest shame; that he was in fact a flesh and blood, breakable and malleable, human being.
Those memories of the torture haunted him in the quietest hours of the night when he lay awake thrashing and tossing in his bed. After spending so long being denied a basic need for sleep, he found his sleeping pattern irregular and even when he was exhausted, some part of his brain refused to shut down, as though still reared up like a snarling guard dog against the torture he had been trained to expect the moment his eyelids closed. Sherlock lay awake in his bed, the sheets strewn around him messily from where his limbs thrashed and crawled when the nightmares overtook him. No matter how much he tried to force the memories out of his mind palace, they replayed on a never ending loop of agony.
The skin on his back was a masterpiece of harsh yellowing bruises, blood blisters, burn scars from where his tortures extinguished their cigars on his flesh, thick knotted scars from whips and knives, and peeling, dying skin encircled the edges of all of his wounds.
And yet, even though his broken skin lingered as a reminder of the worst pain he had ever felt in his life, the daily aches and pains a phantom reminder of every physical attack launched on his back, the tiny spot of blood on his face put there by one of the few people Sherlock considered a friend was more painful than all his weeks of torture put together.
That small physical injury unearthed an every greater emotional wound, one which left Sherlock in the most vulnerable position he had even been in. He knew in his blood that he needed John's forgiveness like he needed air in his lungs. Without it he could feel his chest constrict with each breathe, his narrow focused mind attaching all its concentration on the realisation that what he had done to John was possibly the worst thing he had ever done to anybody. And while Sherlock was usually one to brush off guilt and disregard the emotions of other people, he was struck by how much he cared about what John thought of him, and how much he needed the validation that John was actually happy he was not dead.
And so he smiled, and so he laughed about his friend's silly moustache, because that was what he felt was right. Maybe if he was a lighter person, maybe if he smiled more and make more social conversation, then people would give him more smiles and kindness in return. Maybe people would see him as more human than they had. Because Sherlock realised he needed that. He needed people to know he was vulnerable. He needed people to know that he was capable of feeling pain, of feeling remorse, of feeling things for other people that weren't just cold and scientific deductions.
He realised he wanted to tell John about his time being tortured. He wanted his friend to see his scars and make a joke about how it was nothing to cover his concern and sympathy. He wanted Molly to bandage his scars and gently rub ointment in the wounds with that light touch of hers, cringing as she felt him wince and apologizing profusely for any pain she might be causing.
Sherlock wanted people to know he was breakable. It was the biggest sacrifice he could make for the people he cared about, to show them how much he needed them.
But Sherlock's smiles and jokes were met with more violence as John attacked him again, drawing more blood and causing more pain in a place even Molly Hooper's delicate fingers could not reach to heal.
As he watched his friend drive off in a taxi with his charming girlfriend, John not even bothering to glace back in his direction, Sherlock gave up trying to stop the bleeding from his nose. The way John had launched him into multiple tables in multiple eating establishments had opened up several of the wounds on his back, and he could feel his blood seeping steadily into his crisp white shirt. He clutched his coat tighter to try and hold in his bandages until he could make it back to Baker Street to tend to his emotional and physical wounds. He almost sent a text to Molly to ask for her help, but he stopped himself before he sent it.
If he was denied sympathy from her as well, Sherlock didn't think he would be able to take it.
Somewhere along the line Sherlock had let himself go; his mind had lost its clear, sharp precision, and he began to let the needs of others become a priority over his own.
So he would keep smiling.
He would get making jokes.
And he would keep his injuries to himself.
He would be the invincible man his friends believed him to be.
He would never let John know just how much pain he was hiding, and how much more he had caused with just a few small words and well placed fists.