The reality of what Mary had done only truly hit him when he went to return to Baker Street several hours later. After leaving the hospital, he had taken himself for a long walk, through the streets near the Royal London to start with, and then round Richmond Park. Then he had returned to the flat to pack clean clothes, wanting to distance himself from Mary as much has he could.

But of course she had made any kind of distance impossible. And when he got back to Baker Street, there she was. Washing up the lunch plates in their kitchen as if it was the most natural thing in the world for her to be there. In the flat that he still thought of as both his and Sherlock's. Intruding into their comfortable bachelor existence and treating it as if it was her home as well as theirs.

'Where's Sherlock?' John asked, as he threw his keys onto the kitchen table with a clatter, trying to keep the irritation out of his voice. He didn't want Mary to know that she had got to him, didn't want her to feel as if she had won. Because she hadn't. Not yet.

'Resting,' Mary replied. 'He's exhausted just from the car journey.'

John nodded, his mouth set in a grim line, aware that he was rapidly losing his hard fought for control. All of the calm that he had achieved on his walk erased in an instant.

'So tell me again why you're doing this?' he asked, deciding that since the conversation had to be had at some point, there was no time like the present. And it would be better without Sherlock correcting his grammar every few seconds, and no doubt backing Mary. 'I thought that we agreed that we needed some time apart. Isn't that going to be a little tricky given your current arrangement with Sherlock?'

Mary sighed, 'Relax, John,' she said. 'I'm his nurse, not his live-in carer. I'll be here two or three times a day to give him his antifungals, sort out his meals and help him out with anything else that he needs. I've no intention of moving in.'

'I can't believe that you're pandering to him like this!' John said, one step away from shouting. 'Can't you see how stupid this is?'

'Why, because you didn't think of it?' Mary replied, sounding irritatingly calm, as if she was talking to a child. 'Look, he was going to come home anyway John,' she said.' At least this way he still gets his medication and I can keep an eye on him. I've told him that if he doesn't go to all of his follow up appointments, and look after himself then the deals off. He's not stupid, but he's also an adult. He has the right to make his own decisions.'

'Even stupid ones?' John asked.

'We all make stupid decisions, John,' Mary said quietly. Holding his gaze for just a moment too long. 'You of all people should know that.'

'Anyway, my work here is done for now,' she said, finally looking away, and then moving quickly to pick up her coat and bag from where she had thrown them over one of the armchairs in the living room. On John's chair, of course, never Sherlock's .

'I'll be back later to check on him and cook the dinner.'

And then the door slammed, and there was just the sound of her boots clattering down the stairs and then she was gone.

...

Even then, it took a few days for John to realise the full implications of what Sherlock, the ever brilliant, ever manipulative Sherlock Holmes had done. He had made it impossible for John to avoid Mary. John had fled to Baker Street, to his past, to his old bachelor life as a sanctuary where he could escape Mary and the baby and all that came with them. Baker Street had always been the place that he had fled to. The one place where he knew that he would always feel safe, despite everything. And that safety had always been related to Sherlock, because John had always trusted that no matter how chaotic his life might be, Sherlock Holmes could always deal with anything that came their way. And he would always keep John safe.

And even when Sherlock had been away for Baker Street, the echo of him had remained. When he had died the first time, or rather when he had gone away, the flat had felt empty, a pale imitation of itself. And John had been unable to bear to stay there. But this time, even with Sherlock in hospital it had remained itself - safe, and home. More home than the house at Kew had ever been. It was the place where Sherlock and John belonged. Where they could close the door and be entirely themselves.

And now Sherlock had returned to Baker Street, but he had brought Mary with him. He had allowed her to intrude into their space, his and Sherlock's, and John couldn't work out which one of them he was more angry with.

There she was, every day from eight o'clock in the morning until ten o'clock at night, despite her reassurances to the contrary. She would sometimes leave for a few hours, but she would be there to set up and detach Sherlock's anti fungal infusion every morning, to cook his meals and bully him into eating them, to plump the cushions on the sofa, do the washing up, send him off for an afternoon nap and even, and this one rankled John in particular, to do his washing and ironing for him, a task she seemed to have taken over from Mrs Hudson. In short, she was the perfect private nurse, and it was driving John insane.

She has taken carer's leave from her job at the surgery to look after Sherlock. This casually mentioned fact irritated John more than he cared to let himself think about, because not only was this unpaid, meaning that Mary was no longer contributing to their joint account, but as a partner in the practice it meant that he would have to shell out towards the additional cost of employing a bank nurse to fill the gap at the surgery.

John had started leaving for work earlier and earlier in the morning, but even then he often saw Mary's car drive down Baker Street as he walked towards the tube. Mary with a flair for achieving the impossible that should have ring alarm bells long before that night at Lennister Gardens, had managed to procure a 'district nurse on call' permit from the local council, allowing her to park wherever she liked, for as long as she liked. Even in central London. It also meant that while he was recuperating Sherlock did not have to run the gauntlet of black cabs, but had his own personal chauffeur for his numerous hospital appointments.

The only bonus of Mary's chaperoning was that Sherlock was complying with his treatment in a way that was almost perplexing in its thoroughness. Until John remembered that Sherlock was still treating getting well like a case. He made little attempt to conceal his frustration at the current restrictions that his body was putting on him. To hunt Magnussen properly he needed more than uninterrupted space to work and a decent internet connection. He needed to be able to do the physical investigation too but his transport wasn't yet up to that level of exertion and he was all too aware of it. Despite this, John's offers to help with the 'scut work' were waved away with irritation.

'There is no scut work, John. That is exactly the issues, as always. There is only careful, meticulous assessment and investigation. Besides don't you have lives to save?' came the snappy reply to his offers of help.

And so John would yet again find himself dismissed. He had hoped that now that he was back at Baker Street, Sherlock might let him help with the investigation. After all, hadn't he always worked with him before? Wasn't that how it was meant to be? And yet now, time and again he found himself shut out. Was Sherlock worried that he would leak something to Mycroft who was still gratifyingly absent, was that it? Did he not trust John enough to let him in on the case?

'Too dangerous,' was all that Sherlock would murmur when John questioned him on it. 'Besides, you have a case of your own I think - repairing your relationship with Mary before your child is born.'

And no matter how John tried to protest, he would be met only with silence, interspersed with the clattering of the laptop keyboard as Sherlock returned to his work.

And that was the new pattern of their days. When Sherlock wasn't eating, resting, or allowing Mary to administer medication via the Hickman line that he now had burrowed into the skin of his chest to allow the six weeks of anti fungal treatment that he needed, he was working. Pouring over his laptop, scribbling notes in the black notebook that he had taken to using while he was still in hospital. John had initially found the use of something so old-fashioned perplexing, but then he realised why Sherlock was doing it. He didn't trust Mycroft not to try to hack his laptop. Or rather he didn't trust that while he had been in hospital, Mycroft hadn't appropriated the laptop and set his best men onto it, installing spyware that not even Sherlock Holmes could detect. Sherlock had taken the thing to pieces within hours of getting back to the flat, and while John had told him it was paranoia, it hadn't stopped him from stripping it back to its circuit boards to try to detect any kind of physical bug or spyware that might allow Mycroft to know what he was up to.

He had installed a file that cleared his search history instantly, and set up a complex system of diversions through various routers to prevent his internet searches being trailed, but still he didn't trust the computer enough to use it to record anything concrete. Instead all of his notes went into the black book. Theories, spider diagrams, all written in some kind of code that John didn't have a hope of interpreting. This of course had the added advantage of ensuring that neither John or Mary knew what he was up to either.

Sherlock's refusal to allow him to help irritated John. He didn't believe the excuse that he wanted John to concentrate on sorting things out with Mary. Because how could he? After everything that had happened? John flitted between irritation, that Sherlock was enough of a child to believe that if he demanded something often enough then it would happen, despair that it meant that Sherlock cared so little for him that he wanted him back with his wife and out of Baker Street, and anger that Sherlock repeatedly refused to let him help with the case.

Did he really trust John so little? Did he honestly believe that he wouldn't be able to keep his mouth shut around Mycroft? And why was this case so different? Why had he allowed him to help with everything else. Even with Moriarty and yet not with this?

'But he didn't include you in the plan,' a voice whispered in John's head. 'He didn't tell you that he was going to jump off that roof, that he was going to fake his own death, he didn't trust you enough to tell you about that. What if this is the same? What if he's going to do something stupid again? To sacrifice himself again?'

But for what? What cause could Sherlock possibly have to sacrifice himself again. But John already know the answer to that.

For Mary. Of course, for Mary. He remembered Sherlock's words, that night in this very room. 'I'll take the case.' It was Mary's case, after all that he was working on. Not just Magnussen's. What had Sherlock discovered in his research about his wife that he couldn't or wouldn't share with John? Why didn't he trust him to know, to help. Or did he care for Mary so much that he would protect her even from John?

Because John had seen the way that Sherlock reacted to Mary, the easy familiarity between them. The small glances they exchanged, the way that Sherlock would smile at Mary in thanks when she left a cup of tea or a sandwich next to him when he was working when John had never got so much as a grunt. The way that Mary would rest her hand on Sherlocks shoulder for just a second while she leant over him to see what he was working on. And he would let her. He would let her see, just for a second, and sometimes John, from his seat on the sofa, pretending to work on his laptop while watching some inane drama on the television would hear the soft murmur of conversation, too quiet to interpret and feel - jealous, that was it. Jealous. Because he wanted that. He wanted that intimacy with Sherlock, he wanted to be the one leaning over his should, helping him as he worked, and yet here was his wife, the cuckoo in the nest replacing him.

And yet he had invited her in. Hadn't he? He was the one who had met Mary and brought her into their lives - first his and then Sherlock's. He was the one who had introduced them, and had wanted them to be friends. And so here they were, the three of them - four if you included the baby - all together in Baker Street. Wasn't this what he had wanted? But he had never, even for a second, considered that he might find himself excluded.

John's frustration grew and grew until one evening, when Mary had lingered even longer than normal and he had wanted to slap her hand away every time she touched Sherlock, even to flush his Hickman line, it became too much.

He slammed the lid on his own laptop shut and threw it on the coffee table with such force that Sherlock looked up from his own screen.

'Is there even any point in me being here?' he asked.

Sherlock gave him that look. That puzzled, slightly sarcastic frown that said that thought John was being somewhere between a child and an idiot, then returned to his work as if he'd just swatted off an irritating fly and nothing more.

John sighed. Sherlock obviously wasn't in the mood for any kind of reasonable conversation,. He knew that he should give up, get out of those four walls and leave them to it. Phone Lestrade, go for a pint and try to forget about Sherlock and Mary and that bloody case. But knowing that and doing that were different things. He found himself unable to pull his eyes away from the sight of Sherlock working. Clicking through search screens with one hand, scribbling hieroglyphics in that book of his with the other.

The depth of his feeling for Sherlock hadn't changed. He admired and was frustrated by the man in almost equal measures, but it was the love that prevailed, no matter how hard John tried to push it away. This wasn't like any of the infatuations or relationships that he had had before. It was deeper, more adult, it was based on years of knowledge, layers upon layers of emotion laid down on top of each other. And not just the friendship, the connection, the affection and more lately the love that he felt, but also the anger, the frustration, the irritation that living with Sherlock brought. John knew Sherlock Holmes. He knew his moods, his habits, he knew the worst and the best of him and he loved it all. It didn't mean that the man didn't still have the capacity to irritate the fuck out of him, but he was worth it. John had made his decision. He wanted Sherlock, just Sherlock, and all that Mary's attempts to insinuate herself back into their lives had done was to highlight the contrast. Because he didn't want Mary here. Didn't want her in Baker Street, in the kitchen, in the bathroom, cleaning up after them, looking after Sherlock. He wanted the clock or rewind five years to the time when it had just been him and Sherlock and nobody else.

He looked over at Sherlock, watched the way his hair, still damp from his earlier shower curled damply against his neck above the collar of his dressing gown. He wanted more than anything to run his thumb along that line, to kiss that neck, to work his way up to his ear, to -

'Cup of tea?' came that baritone voice that John so loved, uttering possibly the least alluring words in the English language after, 'Can you provide a urine sample please.'

'Sherlock did you even hear what I said to you?'

'Something about us being out of Earl Grey but still having plenty of English Breakfast?' Sherlock asked, looking up hopefully.

John sighed and throwing the remote control onto the sofa, stalked into the kitchen like a man resigned to his fate.

As he banged the cup of tea down on the desk next to Sherlock a few minutes later, a tidal wave of tea sloshed over the side of the cup, spilling onto Sherlock's stack of papers. He whipped them up, shook the worse or the liquid onto the floor and then reached across to dry them on John's t-shirt.

'What the fuck do you think you're doing?' John asked angrily.

Sherlock looks up in surprise. 'Drying my notes of course. Preferably before the ink runs. He gave the papers another wipe and considered them, as if calculating evaporation rates and chances of dispersion of ink particles..

'Why not use your own dressing gown instead of my bloody t-shirt?!' John's anger was back and this time he wasn't sure that he could contain it.

'It's silk, John, it wouldn't absorb the water. Besides it would be water-marked,' Sherlock said reasonably. 'Your t-shirt was the nearest available object to dry them on.'

'And that's all I am to you is it? The nearest available object for note drying and tea making?'

There. It was out there. He'd said it. And Mary had gone home for the evening, and wouldn't be returning until the morning. And there he was, inches away from Sherlock, close enough to touch him, close enough to stroke the back of that neck, close enough to kiss him. And he wanted to, so badly. His heart was hammering in his chest as he stared at Sherlock, his glance dropping for just a split second from his eyes to his lips and back again.

And Sherlock - Sherlock did nothing to break that look, he just continued to look at John and in his eyes was - desire, was that desire?

'John, I -' he started to say, but it was too late. John was bending his head towards Sherlock's, his hand reaching out to slip his fingers round the back of his neck, to bury his fingers in the curls there, and they were just as soft as he had always known that they would be. And Sherlock was doing nothing to move away from John's touch.

And the kiss when it came was sweet and gentle, Sherlock's lips soft against his, his hand coming up to cup round John's neck in a perfect mirror of John's own actions, pulling him closer. It was a gentle kiss, a kiss full of promise. And it was over far too soon.

It was Sherlock who pulled away first, dropping his head to disconnect their lips, but he kept his hand cupped around the back of John's neck, his eyes closed for a few seconds as if to capture the moment, before he swallowed, dropped his hand to his side and murmured 'Stockholm syndrome,' before returning his gaze to John's with a new seriousness in his eyes.

'What?' John stuttered, thrown by the sudden change in mood.

'Stockholm syndrome,' Sherlock repeated calmly. 'It's the well known phenomena where a hostage falls in love with their captor. It's thought to be a basic psychological protective measure whereby the individual who has lost control convinces themselves that the situation is their choice. There is also almost certainly an element of enjoying being controlled.'

'I know what bloody Stockholm syndrome is,' John said, and then aware that he was still kneeling by Sherlock's chair, pushed himself up and flung himself back into his chair by the fireplace, feeling rejected, as well he might.

'So you're saying - what - that this isn't real? That everything that I've been through in the last few weeks has made me believe that I was in love with you because I was stuck by your bedside for days on end and I justified it by believing it was a situation of my own choosing.' John buried his head in his hands, feeling like a fool, not wanting to hear Sherlock's answer. He had been rejected. After all this time, all of those moments in the hospital when he had been so sure that Sherlock saw him as more than just a friend and his colleague, here was the man that he loved telling him that everything that he felt was a psychological reaction to a traumatic situation.

He felt the air shift in the room, and when he took his hands away, Sherlock was sitting opposite him, considering him, analyzing in that way that John knew so well. But there was something else in his eyes as John raised his eyes to meet them. There was concern, and - regret. Or was John imagining it just as Sherlock seemed to think that he had imagined everything else?

Sherlock gave him a half smile before saying, 'Oh I think it's a lot more complicated that that. Still it's fascinating don't you think?' Sherlock templed his hands and stared at John over his fingertips before continuing.

'A man discovers that his wife is not who he thought that she was. He discovers that she has been lying to him - about her past, about her present, about what she is capable of. He discovers that he is married to a woman who he now believes to be a stranger. He also discovers that she has shot his best friend, a man who he believed to be dead for the best past of two years. He feels guilt for bringing the two of them together. He is doubly invested in his friends recovery - both because if his friend dies of his injuries then his wife will be a murderer - and because having mourned his friend once he has no wish to do so again. Furthermore without his wife, who he believes he is now irrevocably separated from, his friend represents stability and an opportunity to return to his previous way of life.

'Given these circumstances and the rejection that he feels romantically, is it any surprise that he should believe that his protective instincts towards his friend are something more than simple friendship and to view a future in which they are romantically involved as the best possible outcome of an extremely difficult and traumatic few months?'

Sherlock delivered this blistering psychoanalysis in a calm, measured tone. Could he really be this logical, even now?

'So that is what you think isn't it?' John asked, searching Sherlock's eyes for some sign of emotion. For something, anything that would indicate that this wasn't what he really thought. That this was just another game. 'You honestly believe that my feelings for you are just a psychological reaction to a set of difficult circumstances?'

'Don't you? If you think about it logically?' came Sherlock's reply, and his eyes were impossible to read, even for someone who knew him as well as John.

'Logical? You want me to be logical?' John didn't know whether he wanted to laugh, cry or scream, but even as the words left his mouth he knew what Sherlock's reaction would be.

'Always,' his friend murmured. And the sadness in that single word wasn't something that John could have imagined. That one word gave him hope. That this situation was not lost after all.

John took a deep breath and considered. What the old John, the soldier John who acted on impulse wanted to do was to jump up, slap Sherlock round the face like a Victorian heroine and walk out the door, slamming it as loudly as he could behind him. But he was neither a Victorian heroine or a teenager so instead he sat, templed his own hands in a conscious reflection of Sherlock's own body language and tried to think like Sherlock Holmes.

'So let me get this straight,' John began. 'My guilt about Mary's actions made me your prisoner, your hospital room my prison, and I was so conflicted by my own emotions that I believed you to be entirely in control of my life from that moment on?'

'Precisely.'

John surveyed his friend. Something was off. His skin was still pale, with the greyish tinge of a man who has not seen sunlight do a long time. His blue dressing and the grey t-shirt underneath hung from his thin frame. His pupils were constricted from the buprenorphine that served both as pain relief and to reduce the desire to abuse heroin again. Sherlock Holmes was still not a well man, but there was something more. He was a conflicted man. What if he wanted to be convinced? What if this was after all a test? Because after all, Sherlock was a man of logic and not emotion. Declarations of love would not win him. But logic just might. John cracked his knuckles, smiling slightly as Sherlock winced, and settled in for the fight.

'So how do you explain the fact that I was in your hospital room day after day, before I discovered that Mary was the one who had shot you?' he asked

'You were with me. You heard the shot. You felt responsible for me because you wrongly believed you should have stopped me going into that room alone and because,' and here Sherlock paused here for effect, 'you escaped uninjured.'

'Ah, survivor's guilt!' John exclaimed, wondering exactly how many psychological theories Sherlock could bring into this one conversation. 'Of course. That was what it was. I felt guilty that it was you who had been shot and not me. So emotion had no part in this? Is there no possibility that I genuinely cared for you and couldn't bear the thought of losing you again?'

Sherlock waved his hand dismissively. John had to yet again resist the temptation to thump him. Strange how anger seemed to be an easier emotion to deal with than love. But then it was after all the one that he had far more experience of.

'Friendship, John. Fratros, brotherly love, not the Eros of romantic love.' Sherlock said, shaking his head slightly. 'You love me as a friend, not as a romantic object. You confused one with the other, that's all. Easy to do when you are trapped in an intensively emotional situation.'

John stared at him, his attempts at logic obliterated by this one simple statement. If what he felt was not what he thought that he felt then where did it leave him? But he loved Sherlock, he knew that he did. He loved the man body and soul, and as far, far more than a friend. It had just taken him a long time to realise it. But how could he explain that to Sherlock, a man who ran his life on facts and logic. And what did it matter if Sherlock didn't feel the same way about him?

Sherlock regarded John for a long moment, hands resting in his lap now, his pose calm and possessed. 'I am truly sorry, John,' he said finally, 'If I have made you want something that you cannot have.'

The implication of what he was saying took a while to sink in.

'Because you don't want me,' John said, heavily, closing his eyes, not wanting to see Sherlock's expression when he admitted that that was exactly the problem. But the answer that came was not the one that he had expected.

'That's irrelevant,' Sherlock said.

Not 'No,' or 'I'm sorry, John,' but, 'That's irrelevant.'

'Irrelevant How can it be irrelevant?' If John had been confused before then he was truly confused now.

'Because what you think you feel is built on a lie,' and there was that logic again. But behind it - regret.

John shook his head and stared at his hands, turning them over as if he might find some answers in them. Sherlock stood and walked to the window, had John been watching he would have seen the effort that those steps took him.

'You think that I don't know you?' John said finally.

'Oh, I think that you do know me. You know the Sherlock Holmes that I project to the world. But you don't know what I've done, you don't know how dark I've gone in the past. If you knew that, you wouldn't want - whatever it is that you think that you want.'

'I don't care what you've done,' John said. 'I would love you anyway.'

'You would care, John,' Sherlock said, turning to look at him. 'You would care very much, and you would hate me for it.'

John went to stand, to go to him, to prove that it didn't matter, but Sherlock stopped him with a hand. 'Don't,' he said quietly. 'It's better like this,'

'Better for who?' John asked.

'For both of us. You don't want me, John. You want an idea of me. You want the Sherlock Holmes who has spent the best part of the last two months lying in a hospital bed, vulnerable, broken, in need of protection. That's what you love don't you see? A version of me who needs looking after, who you can be Dr Watson to, who you can control. Because you and I both need to be in control, and that is why this is not a subject that we should ever discuss again.'

'You think that's how I see you?'

'I think that you have known me for a long time without entertaining romantic feelings towards me,' Sherlock said. 'And I do not want to be loved for being a broken man. Because that is not who I am. Nor do I need a protector.'

'So what do you need?' John asked watching him as he stood silhouetted against the light streaming in from the windows, trying not to think about how beautiful he was.

'I need a friend, John,' Sherlock told him softly. The best kind of friend, the kind of friend that I trust with my life.'

'But that's all?'

'No!' Sherlock came towards John, knelt by his chair, put a hand on John's shoulder and gripped it tightly. 'I told you once that I didn't have friends, I only had one. Do you remember?' His voice was low and urgent and cut through the confusion of John's thoughts.

John nodded, not trusting himself to speak. Baskerville. The churchyard. The time that he had seen Sherlock Holmes doubting himself for the first time.

'You are, and I hope will always be my first and best friend,' Sherlock said. 'Don't underestimate that. The Greeks talked about three kinds of love - Fratros, Eros and Agape. Of those Agape, the love that existed almost entirely between two men, a spiritual love that transcended bodily desires was the highest. That is what I ask from you.' His eyes sought John's, caught them and held them.

'Agape,' John murmured, unsure if he had been handed a diamond or a consolation prize.

'Precisely. That is what I need from you, John. Can you give me that?'

John looked at Sherlock, at the man that he loved, and saw something in his eyes that he could not identify. An odd combination of pain, regret and desperation that he could not put a name to. But he did what he always did. He gave Sherlock Holmes what he needed, and so he nodded. 'If that's what you need,' he murmured. 'Although those Greeks, from what I remember of their friendships...'

'But we are not Greeks, John,' Sherlock said. Touching his forehead to John's for a brief moment before offering him his hand and pulling him up into a manly hug.

'Now go and talk your wife,' he said, clapping John on the back. 'Remind yourself why you fell in love with her in the first place. Because she's still the same person that she always was. And I made a vow remember? To protect the three of you. Don't make me break that promise.'

John walked towards the door, shaking his head, trying to process it all. 'You want us to be the family, that you can't have?' he asked, hand on the door handle.

'No, I want you to be the family that I do have,' Sherlock said, sittting down at the desk and opening his laptop. 'Now go away, I've got work to do.'

And if John had looked back before he closed the door behind him, he might have seen Sherlock Holmes sitting there, head buried in his hands, as if he had just thrown away the most precious thing in his life.

But instead he closed the door softly behind him and headed home to Kew, and his wife, and his as yet unborn child. Because that was what Sherlock Holmes wanted him to do. And because he was John Watson, and he had had a lifetime of serving a higher purpose. And for now, and for always, that higher purpose would be Sherlock Holmes.

Agape. It wasn't what he wanted but it was enough. For now.

And so that's it. Apart from the epilogue that will be along shortly.

It may not be the story that some of you wanted or expected, but I'm hoping that it feels true, and real, and fits in with the canon as it stands. I wanted to explain that scene at the airfield, and the affection between Sherlock and Mary, but also the way that John and Sherlock interact at Appledore and before.

There is no doubt in my mind that Sherlock loves John. It's there all the way through series 3, in those small glances that he gives him, in the way that he acts around him, even in those ridiculous napkins that he folds. And yet he gives John back to Mary because he made a vow, and because he believes that it is the right thing to do, and because almost without him realising, John Watson has transmitted his moral compass to Sherlock.

And so this is how this story has to end. With John on his way to reunite with Mary (although we assume that it doesn't go smoothly and hence Sherlock organises Christmas at his parents house to give them the final push to get back together as well as giving him the opportunity to steal that laptop from Mycroft). And with Sherlock yet again alone, and trying to find a way to protect the three people that he has pledged himself to keep safe.

Is it what he wants? Almost certainly not. Is this the end of John and Sherlock's story? You'll just have to wait and see...