Well what a ride! Here is the last chapter (for now) of this story. I've already started writing the season 4 of the show but it'll be a while until all the pieces fit together. But don't worry! This fic will not be abandoned. And you might get an extra chapter after this one with the end of HLV and beginning of TST.

But for now, I'd like to thank my amazing, wonderful beta nightgigjo. Nothing about the last chapters would have been as good as they are if it wasn't for you.

As always, thank you to those of you that read, favourited, followed or reviewed the last chapter.

Disclaimer: All the characters displayed in this fic belong to their respective creators, JK Rowling (Harry Potter), Moffat and Gatiss (BBC Sherlock), and Sir Arthur Conan Doyle (Sherlock Holmes).

Note 08/03/2021:Edited.

Chapter 18:His Last Vow Act IV, Denouement.

Hermione drew her woollen jacket tighter around her frame and rubbed her arms, trying to stay warm, leaning back even further in Sherlock's black armchair. She closed her eyes. There was a wariness, a tension that had seeped into her body during the past months and she couldn't shake, no matter how much she slept. On the table was the tea she had made when she had arrived, already cold. Mrs Hudson had gone away a few days ago to spend the holidays with her sister, and neither John nor Sherlock had bothered to light the fire or turn on the heating. Hermione had not seen much of the older woman lately. When Sherlock had been admitted to the hospital the second time, John had packed an overnight bag and moved back to his old room. His excuse—which Mrs Hudson had not fully believed, Hermione thought—had been that Sherlock might need a doctor close, just in case. Hermione and Mary had dropped by every now and then, but the visits were always short-lived, as Sherlock spent all his time inside his head and John had no interest in talking. He had assured Mrs Hudson this was a temporary arrangement. Nevertheless, the months had gone by, Sherlock had been given the medical all-clear, and John was still living there, and Hermione was still sleeping in a small twin bed at Mary's.

The front door opened, and someone rushed up the stairs, shouting Sherlock's name. Hermione stretched, her bones groaning and cracking. Moments later, John hurried into the living room, out of breath. He stared at her and noticed the mobile phone in Hermione's hand. Letting out a disbelieving snort, he tore off his jacket.

'Where's Sherlock?' asked John.

'Out,' said Hermione. 'He's managed to convince Lestrade to let him go to a crime scene.'

'He's convinced Greg?'

'I helped a little. Sherlock's mostly recovered, and it's a minor B&E. He's probably looking for this now,' she said, lifting Sherlock's phone before leaving it next to her mug.

John went into the kitchen, and from one of the shelves, pulled out a bottle of whiskey. 'Shouldn't you be packing your bags?'

'I haven't fully unpacked since I arrived at your house.'

John nodded, and without looking at her, took a long swig from his glass as he headed down the hall.

'Well, I do. If you excuse—'

'John, please.' John stopped in his tracks but did not face her. 'We can't keep like this forever.'

John swung around and walked over to her. 'What do you want me to do? Hmm?'

'Face the situation. Magnussen is not going anywhere, and Mary is never going to stop being a former assassin. What's past, it's gone. What are you going to do now?'

'What choices do I have?'

'Either you are in, or you are out,' answered Hermione. 'What have you done with it?' John sighed and went to Billy on the mantle. Lifting the skull, he took a flash drive out from under it and gave it to her.

'I haven't even opened it. I haven't had the courage to do it.'

Hermione observed the flashdrive briefly. He had not read it; she believed that, but he had toyed with it for quite some time. The permanent marker had faded.

'You don't have to.'

'What if I want to know who I am married to?' His voice grew harder and louder.

Hermione took John's hand and closed his fingers around the memory drive. 'You're married to Mary Watson. To the woman you fell in love with, to the mother of your child. To my best friend.'

'She almost killed Sherlock. And for what I understood, he wouldn't be her first one.'

'She's not the only one who's killed someone,' rebated Hermione.

'It's not remotely the same,' John ripped his hand away from her and stood behind his armchair, trying to get some space between them. 'You know, I thought all of us, you'd be the angriest about Mary hurting Sherlock.'

Hermione sighed. 'Did he tell you?'

'He didn't have to. Contrary to what you all seem to believe, I'm not blind.'

'John, I'm not justifying her actions.' John cut himself from speaking, and Hermione continued softly this time. 'Neither I'm justifying her motives. I don't know if I share Mycroft's opinion of sentiment being a weakness, but it definitely is a vicious motivator. I—I understand Mary. To a deeper level that I'm not sure a lot of people do. Our lives have been plagued by heartbreak, by becoming tools of opportunity because it was the option we had at the moment. She made the choice of leaving it all behind, and without expecting anything, she found you and the life you offered. Magnussen was threatening to take it all away, and in a sense, he's won.' Hermione took a deep breath. 'Look, John. We are not like you. You might have been able to rationalise it, find a different way out. But Mary, me… Sherlock. You know him. What do you think he would have done to keep everyone safe?'

Those words, at least, seemed to sink in, and John pocketed the flash drive.

'We have all done things we are not proud of. I know it; you definitely know it.' Hermione concluded. 'Do you still love her?'

'I wouldn't be here if I didn't,' he answered with a quavering voice.

'Isn't that what matters? You cannot change the problems of her past. You cannot deal with them; you cannot solve them. But what happens from now on? That's up to you. Maybe spending Christmas with the Holmes is what we need. A quiet Christmas, after everything that's happened, will do us good.'

Hermione left John before Sherlock returned. She had called Mycroft a coward, but she was not much better. After the brief conversation at the hospital, Hermione had avoided being in the same room as Sherlock. It wouldn't have been difficult to get him alone: her job was hanging by a thread, and she was not even sure if she was still in the mission roster; John kept a regular schedule, and Mrs Hudson could be persuaded to leave for a short while. But she hadn't done any of it. Instead, she had camped out in Mary's spare room, lived with the contents of the suitcase she had managed to pick, and decided that whatever had been left unspoken between her and Sherlock could wait. The world around her was a collapse hazard, and she had invested every ounce of her energy in keeping it together.

The day after, a gleaming black car picked Mary and Hermione and delivered them to a quaint red house in the Cotswolds. The stone fence, the cast iron little door, the chimneys blowing the smoke from the fireplaces. It was something taken out of a postcard, including the smiling hosts who came to greet them. As Hermione was hugged by an elated Margaret, she could see behind her, inside the house, the rest of the invitees. Yes, the place and its owners were the perfect picture of provincial life. The guests were not as picturesque: their children, the Government and the detective, and their friends: an assassin, a secret agent, a junkie called Billy, and John. But Siger and especially Margaret had decided not to let anything ruin the occasion and had asked politely about Billy's last "workplace", about the baby and Hermione's "handsome" father, while (matriarca) passed some punch around. Hermione accepted it cheerfully and glanced sideways at Sherlock, who shook his head at his mother. He had been uncharacteristically quiet, and Hermione had started to think that was never a good sign. Mycroft approached his brother, and both of them stepped out of the house. Hermione followed them until the door closed, an unsettling feeling taking root in her head.

Outside, Mycroft took a puff on the cigarette his brother had given him, coughing. 'This isn't agreeing with me. I'm going in.' He dropped the cigarette onto the path and stepped on it. Sherlock turned to mock him, but he saw his brother had stopped in the middle of his walk to the house and was staring through the window. On the other side, Hermione was sitting next to Siger Holmes, a smile dancing on her lips as she sipped her punch. Sherlock observed his brother.

'You love her.'

Mycroft inhaled deeply and glanced at him. 'Despite what you might think, Sherlock, I am not immune to the stings of love. I just prefer not to dwell on them.' He paused briefly, before adding more seriously. 'After all, life is about choices.'

Sherlock watched him, impassive. 'What does that mean?'

'Eventually, we all have to choose. Including you. And choices have consequences.'

'Is that a threat?'

'It's a warning, brother mine. Remember who she is, and more especially, who you are. Casualties are not uncommon, and you do have a knack for perilous situations.' Sherlock did not answer. 'Hermione and I haven't seen eye to eye recently. I think I've let her down more than she deserves.' Mycroft turned away from him. 'But we do have a thing in common, Hermione and I. Your loss would break our hearts.'

Sherlock, who had just started to take a drag on his cigarette, choked on it. 'What the hell am I supposed to say to that?!' he sputtered, bewildered.

Mycroft held out his arms a little. 'Merry Christmas?'

'You hate Christmas.'

'Yes. Perhaps there was something in the punch.'

'Clearly,' Sherlock scoffed. 'Go and have some more.'

Mycroft went up the steps, opening the door. Sherlock spared a look at Hermione. In that instant, she raised her head and saw him, and her smile grew wider if that was possible. He felt his stomach turn on itself, and his heart double its beating. These physical reactions made it hard to ignore that his sentiments had gotten the best of him. What he had told her in that fateful night when she had fled Baker Street, and he had started this macabre dance with Magnussen, had not been entirely a lie. She had taken control of some corners of his mind palace he was not aware they existed. Everything that made her special to him had been exposed in a display modelled after the ones holding the crown jewels, to be studied, observed, and Sherlock suspected, worshipped. But none of that mattered now. Because he was going to give her yet another reason why whatever they had was bad news. Sherlock took the last drag from his cigarette, staring at the sky, a gush of air ruffling his hair. Mycroft was always right.

There was an east wind coming.

'Don't drink Mary's tea. Or the punch,' yelled Sherlock from the hallway. John left Mary on the couch and ran towards the door where Sherlock was grabbing his scarf from the peg, only to disappear again into the next room, where Mr Holmes was lying half collapsed on the sofa with Hermione by his side. Sherlock held a hand over his father's nose and detected breathing, steady and calm. Relief ameliorated the sting of guilt he felt more often than not these days. Moving to Hermione to the same with her, something about her peaceful face made him stop. She was exactly like the picture his eidetic memory had stored in his brain. He checked on her, and his hand moved on its own, one lonely finger trailing over her cheek. Her skin was also as soft as he remembered, and he could almost see the golden sparks by the sun on the brunette tresses between his index and thumb. On any other occasion, he would have been confident about his possibilities. But with Magnussen, this might as well be the last opportunity he had to be this close to her. He clenched his fist and turned around to the kitchen when he heard John's steps coming closer.

'Sherlock?' John came in, walking past Billy, while Sherlock checked on his mum, asleep in the armchair. 'Did you just drug my pregnant wife?'

Sherlock moved to his brother, slumped on a dining chair with his head on the kitchen table and one arm protectively over his laptop. 'Don't worry. Wiggins is an excellent chemist.'

'I calculated your wife's dose meself,' the young man confirmed. 'Won't affect the little one. I'll keep an eye on 'er.'

'He'll monitor their recovery. It's more or less his day job.'

John stared at him. 'What the hell have you done?'

Sherlock took a moment to reply. 'A deal with the devil.'

Realisation flashed across John's features. 'Oh, Jesus. Magnussen, isn't it?'

John left the kitchen, and Sherlock pried the laptop free from his unconscious brother's hands. John came back at the same time. The sound of an approaching helicopter broke the cottage's quietness.

'Ah. There's our lift.' Sherlock said simply and walked outside the kitchen to the small garden, John following him with his coat in hand. A helicopter flew low past the front of the house, landing on the grass field. John just stared at it, bewildered. Before he could ask, Sherlock addressed him tensely. 'D'you want your wife to be safe?'

'Yeah, of course I do.'

'Good, because this is going to be incredibly dangerous.' Sherlock turned to the helicopter, sputtering, with Mycroft's laptop safely secured under his left arm. 'One false move, and we'll have betrayed the security of the United Kingdom and be in prison for high treason. Magnussen is quite simply the most dangerous man we've ever encountered, and the odds are comprehensively stacked against us.'

'But it's Christmas!' complained John.

'I feel the same.' His grin faded when he saw John's expression. 'Oh, you mean it's actually Christmas. Did you bring your gun as I suggested?'

'Why would I bring my gun to your parents' house for Christmas dinner?!'

Sherlock was holding out the coat in his right hand. 'Is it in your coat?'

'Yes,' John replied tetchily, taking it from him. Sherlock smiled and started walking towards the helicopter, John following suit. 'To Hell, then.'

From the helicopter, John and Sherlock saw the imposing glass and metal structure of Appledore. In all its beauty, the house had a somewhat sinister vibe, like a mousetrap. And, of course, it was heavily guarded. The security detail was everywhere, some of them with visible weapons, others presumably with them hidden. They landed in what John thought should have been the front yard in any other house while he saw several men coming towards them. During the short flight, Sherlock had succinctly informed him that everything from the moment they arrived would be designed for two purposes: power and intimidation.

Sherlock had not been far off the mark, and even with his warning, John did feel the pressure of Magnussen's vast resources. The whole aesthetic, white and sparingly decorated, gave the impression of being inside of a lab, one which they weren't the scientist but the rats. Sherlock, on the other hand, showed no signs of being impressed.

The men were led to an indoor lift which took them to a pristine white room. A large white sofa occupied the length of a varanda, and Magnussen sat on it, nursing a glass of something. Sherlock stopped a couple of paces in front of the sofa while John stood several feet away from him. Magnussen nodded to his men, and they left.

'I would offer you a drink, but it's very rare and expensive.' Magnussen drank, and Sherlock sat to his right, keeping his distance. Sherlock sighed and put the laptop between himself and the other man. He was staring ahead, his eyes focused at some point behind John's back. Calmly, he crossed his legs and clasped his hands on his lap.

'It was you then.'

John glanced over his shoulder. Projected onto a wall, there was the footage of Sherlock's and Mary's rescue of John almost a year ago. He turned and walked towards the wall, watching the images repeating in a loop.

'Yes, of course,' said Magnussen. 'Very hard to find a pressure point on you, Mr Holmes. The drugs thing I never believed for a moment. Anyway, you wouldn't care if it was exposed, would you?' Magnussen's mouth quirked in a sardonic smile as the images played. 'But look how you care about John Watson. Your damsel in distress.'

John spun around and walked closer to Magnussen, his voice tight and furious. 'You ... put me in a fire...for leverage?'

'Oh, I'd never let you burn, Doctor Watson.' Magnussen sat up and put his glass onto the clear table in front of him. 'I had people standing by. I'm not a murderer...unlike your wife.' The older man stood up, and John stared at him grimly. While Magnussen walked over towards the wall and, sliding a finger across the glass, the footage disappeared. 'Let me explain how leverage works, Doctor Watson. For those who understand these things, Mycroft Holmes is the most powerful man in the country. Well...apart from me.' The side of Sherlock's mouth lifted a fraction. 'Mycroft's pressure point is his junkie detective brother, Sherlock. And Sherlock's pressure point is his best friend, John Watson. John Watson's pressure point is his wife. I own John Watson's wife…' He approached the couch again and sat down, looking at Sherlock. '...I own Mycroft. He's what I'm getting for Christmas.' He held out his hand towards Sherlock, who shoved the laptop across the sofa towards him.

'It's an exchange, not a gift.' Sherlock stood up while Magnussen raised his eyebrows at him. Sherlock walked towards John and then turned around again. Magnussen picked up the laptop.

'Forgive me, but…' He held the laptop to his chest and ran a finger over the back. '...I already seem to have it.'

'It's password protected. In return for the password, you will give me any material in your possession pertaining to the woman I know as Mary Watson.'

Magnussen grinned. 'Only Mary Watson?'

Sherlock frowned and glanced at John. Magnussen let out a small chuckle as he shook his head. When he stopped laughing, he fixed his attention squarely on Sherlock. 'You know, I honestly expected something good.'

'Oh, I think you'll find the contents of that laptop—'

'—including a GPS locator. By now, your brother will have noticed the theft, and security services will be converging on this house. Having arrived, they'll find top-secret information in my hands and have every justification to search my vaults. They will discover further information of this kind, and I'll be imprisoned. You will be exonerated and restored to your smelly little apartment to solve crimes with Mr and Mrs Psychopath. But you are right, Sherlock,' said Magnussen. 'There are some things in this computer that you'd find very interesting. If you knew, what kind of secrets your brother has…"

Sherlock ignored the baiting. 'The fact that you know it's going to happen isn't going to stop it.'

'Then why am I smiling?' He looked up at Sherlock, and before the detective could say anything, Magnussen stood up slowly, buttoning up his jacket. 'Let me show you the Appledore vaults.'

He led them across the room and through the open glass doors of a study. He walked to a set of wooden doors at the side of the room and then turned back, putting a hand on the handles.

'The entrance to my vaults. This is where I keep you all.' He made emphasis in the last word before pulling the doors open, revealing a brightly lit room, empty but for a black leather armchair. Magnussen stepped into the room and sat down in the chair. Sherlock quickly skimmed around the room, searching for a concealed door. But the room had no rug, no shelves or decoration. Nowhere to hide a trapdoor.

'Okay—so where are the vaults, then?'

'Vaults? What vaults? There are no vaults beneath this building.' Magnussen answered John, and gestured around the room. 'They're all in here.'

Sherlock realised what Magnussen meant before he leaned forward and raised hid finger to touch his temple. Besides him John blinked, confused.

'The Appledore vaults are my Mind Palace. You know about Mind Palaces, don't you, Sherlock? How to store information so you never forget it—by picturing it. I just sit here, I close my eyes—" He did so, slowly lowering his head. '—and down I go to my vaults. I can go anywhere inside my vaults...my memories.' He turned his head from side to side. 'I'll look at the files on Mrs Watson.'

Sherlock and John stared at Magnussen, watching the man raise both hands, his fingers flickering in front of him as if working his way through files inside an imaginary drawer. Magnussen began humming idly to himself. He lifted his right hand as if taking a folder out of the drawer. 'This is one of my favourites.' He sat back in the chair. He moved his hands as if he was turning the pages inside the file. Sherlock lowered his head, while Magnussen chuckled quietly. 'All those wet jobs for the CIA. But this is not the most interesting cabinet in the room.' He made a gesture of depositing the file back in the drawer, closing it, and then turning slightly to the right. He put his hand flat as if caressing a surface. 'You see, I have this new one, shiny, polished wood… Recent acquisition. The papers inside still smell like printing ink. There are some initials engraved on the first drawer: H.J.G. Any ideas, gentlemen?'

Sherlock's blood pumped on his ears, and John gasped. Of everything he had thought might go wrong, every plan B he had created inside his head, Magnussen knowing about Hermione had not been one of them. Mycroft had made sure to protect her, not too well, apparently.

'Hermione Granger—or Black as she goes these days—a.k.a Salem for those in the MI-7.' He opened his eyes and smirked at the men. 'You see, Mr Holmes, I had some…inside information about you. Someone who knew you very well. Sadly, Moriarty did not know about this very particular person. But then, Mrs Watson shot you, and of course, I was keeping a weather eye on you. To my surprise, this exquisite brunette came barging in at the hospital, demanding to see you, almost knocking over one of my men.'

The Cheshire grin on Magnussen's face was demented and lascivious. 'What a sight for sore eyes she was. The fire in her was a sight to behold. And those wet clothes! I myself have revisited that view in a more private setting.'

Sherlock stood there, his brain fighting against the fog of rage that was starting to cloud it. He could not afford rage. He needed clarity. But he was finding clarity challenging when all he wanted to do was take the steps that separated the two of them and punch Magnussen in the face.

'But my informant didn't have anything on her. Not a name. Not a photo. I admit it was…careless of me, to think Moriarty's information was all there was to it, but well… You used to be 'the Virgin' if I recall correctly. Not anymore, I guess. So, who was this gorgeous woman who left the hospital and went straight to the Diogenes Club? Maybe the Holmes brothers have finally agreed to share their toys?'

Magnussen chuckled to himself and stood up, closing his jacket. 'I am an overachiever, always have been. The more information on you, the better for me. So, I researched her. Her data was awfully protected, but again… Everyone has a price.' The Swede went to his bar and poured himself a glass of bourbon. 'As it turned out, to my delight, Hermione Jean Granger has so many secrets, big ones that should be kept away from people like us. But this is not news for you, right, Sherlock? Nor for John or Mary... And you know what happens to anyone that threatens their secrets. Does Azkaban ring a Bell, Mr Holmes?'

Sherlock remembered a conversation from long ago. A lengthy explanation by the fire, after a nightmare, about a structure in the middle of the North Sea, aforetime populated by soul-sucking creatures. Although those creatures had disappeared, the prison was still the worst nightmare for magical folk and the most fearsome punishment.

'It's all about knowledge,' Magnussen continued. "Everything is. Knowing is owning. So, what to do with all this unexpected information? I place the pieces on the board, with one shiny new, unexpected piece.' He pointed to a chessboard. He touched the king with his finger, moving it from side to side. 'Your brother is the king in this little chess play of ours, Mr Holmes, the master key to the British empire. You are the bishop, flanking the king, doing his dirty work. John Watson, Mary Morstan, Gregory Lestrade, all of them are nothing but pawns but... What is Hermione Granger?' He took the white Queen, playing with it in his hands, and put the top of the figurine on his lips. 'Oh, she is the Queen… You own the Queen, you can do whatever you like to the pawns. In the end, I did not even need Mary. All I needed was Hermione Granger, and then the rest of the pieces would fall like dominoes. The key to the government. So as long as I have this information with me, Hermione is mine, and therefore, so are all of you. I could even give you all the information on Mrs Watson; I don't need it anymore. I could ask you to lie on the floor and lick my shoes clean, and you'd do it because the alternative…'

Sherlock's brain was trying to find a way out of this situation, and coming up with nothing. He has gambled everything to Mycroft arriving and somehow sorting everything out, because it was something his brother could be trusted to do. But this changed everything.

'So there are no documents. You don't actually have anything here,' said John.

'Oh, sometimes I send out for something…' Magnussen lifted his left hand and looked down at his watch. '... if I really need it...But mostly I just remember it all.'

'But if you just know it, then you don't have proof,' John insisted.

'Proof? What would I need proof for? I'm in news, you moron. I don't have to prove it—I just have to print it.' Sherlock lowered his gaze, fully aware of how badly he had miscalculated. Magnussen downed the contents of his glass. 'Speaking of news, you'll both be heavily featured tomorrow—trying to sell state secrets to me. Oh! But before you get to jail, make sure your brother knows about who owns his little whore… Or should I say yours?' He tutted disapprovingly, then glanced at his watch again, walking out of the room. 'Let's go outside. They'll be here shortly. And I can't wait to see you arrested.'

John watched Magnussen go, then stepped closer to his friend and murmured to him. 'Sherlock, do we have a plan?'

Sherlock was fixed in place, his gaze lost in the marble floor. He had been outsmarted, but not Everything was lost. He had one last opportunity to keep Mary, John, Hermione — and despite his reluctance, Mycroft was safe. He had no big brother, no Government to clean up the mess he had led himself and others into.

It was time for him to slay a dragon.