John sat with his forehead resting against the window of the cab, appreciating its coolness, needing the physical sensation of it to anchor him to reality in a world that suddenly seemed to be imploding.

He had never in his life wanted Sherlock to be wrong more.

Because Sherlock was wrong - he was often wrong. In fact, when John really thought about it, he got it wrong more often than he got it right.

But he always got it right in the end - always. And this, John had an uncanny feeling, was the end.

He had no idea where he was going. Sherlock had told him only that there was a black cab waiting for him outside, and he had numbly walked down the stairs of 221b and got into the back of it. The cab driver had proved strangely unchatty for a cabby - confirming that he was here for John, but refusing to divulge their destination. And John had been too tied up with his own thoughts to notice the dark streets that they were driving through.

He sat up and forced himself to concentrate. They were on the Westway. On his left he could vaguely see the tower blocks of St Mary's Hospital and beyond it, the dark shape of Paddington Station. Then the cab turned left, towards Bayswater. John sat back, wondering where on earth Sherlock was taking him.

'Do you trust me, John?' he had asked.

'Sherlock, where are you?'

'Theres a cab waiting outside. Get in, don't ask any questions. It will bring you to where I am.'

'Mary -'

'It isn't what you think.'

'Then what is it?' he had hissed, very aware of Mrs Hudson standing in the kitchen behind him, pretending to be invisible but listening hard all the same. 'Explain this to me Sherlock.'

'Not now. Get in the cab, John and you'll hear everything that you need to know.'

John had gone through every possible permutation in his head, but one fact remained. His wife, his beautiful wife, his beautiful intelligent, wife had shot his best friend and then disappeared, like a shadow.

'Like an assassin' whispered the voice in his head. Because not only had his wife shot his best friend, she had been in Magnussen's office. She had broken into Magnussen's office - one of the most secure locations in the country. She had knocked out a security guard, knocked out Janine, and turned a gun on Charles Augustus Magnussen. Why for heavens sake? Why on earth would she do that? Who was she? What was she? And why the hell hadn't he realised before that there was something odd about this beautiful, intelligent woman choosing him, John Watson. Had she just married him to get to Sherlock? And if so then why hadn't Sherlock worked it out? Sherlock liked her, for heavens sake. Had she fooled him too?

Buried in his thoughts, John hadn't even noticed that the cab was slowing down until it drew to a halt outside a row of white-fronted buildings and the interior light came on, bringing John back to reality with a jolt.

'Eighteen quid please, mate.' The cabby was saying. Of course, Sherlock might have organised the cab but heaven forbid that he would actually have paid for it.

John scrabbled for his wallet and pulled out a twenty pound note. Handed it to the cabby. 'Keep the change,' he murmured out of habit, opening the door to the cab and clambering out before turning back to the cabby uncertainly.

'Um - where am I going?'

'No idea mate, sorry, I was just told to bring you here. Middle of Leinster Gardens, he said. Strange place, isn't it? Spooky almost. And noisy too, what with those trains going through the back of the buildings.'

'Thank you,' John murmured, and the cab sped off as soon as he had shut the door.

He stood for a moment, facing the row of houses, wondering where he should go. He jumped at the buzzing of his phone in his pocket.'Straight ahead,' came Sherlock's voice. 'Number 24.'

The door opened as John reached it, but instead of a house, John found himself having to turn a sharp left into a narrow corridor.

'What is this place?'

'No time. I'll explain later. I need you to sit in the wheelchair.'

'What? Sherlock what the hell is going on - and you look like shit by the way. You're the one who should be sitting down. I'm amazed you can even stay vertical.'

'John, I need you to trust me.'

'I do trust you. I just want to know -'

'And I've told you there no time. Our assassin will be here in less than five minutes if all goes to plan. I need you to sit in that wheelchair, stay still and silent no matter what happens, and pretend to be me.'

'You want me to sit in a wheelchair and pretend to be you while the person who tried to assassinate you comes in and has a second pop? Do you think I'm crazy?'

'John,' Sherlocks voice was low and urgent now as he seized him by the shoulders. 'There's no time to explain. Just do as I ask. I promise you that you will be safe.'

And John, feeling more detached from an increasingly surreal situation by the minute did as Sherlock asked. He sat himself in the wheelchair, allowed Sherlock to stick the blind ending drip tube to his arm, turned up his coat collar and ruffled his hair as Sherlock's instructed in a poor approximation of Sherlocks curls.

'Put this in your ear,' Sherlock said, handing him a tiny earpiece. 'You will be able to hear our conversation but we won't be able to hear you. I'll be just outside, out of sight. And whatever happens, remember, don't move and don't speak. It's essential that our visitor doesn't realise who you are.'

'What if it goes wrong?' John asked.

'It won't.'

'But what if it does?'

There was a soft buzz in Sherlock's pocket. 'No time, John,' he said, already striding towards the door. 'It's showtime.'

It was only seconds after Sherlock had walked out of the door that John heard a soft click in his earpiece indicating that a call was in progress.

And then he heard Mary's voice, and his heart started racing so fast that he thought it might explode.

'Let him be wrong. Please God, let him be wrong,' he found himself praying, to a God that he had long ago decided almost certainly didn't exist,

'Where are you?' Mary was asking.

'Cant you see me?' Sherlock replied.

'Well, what am I looking for?'

'The lie, the lie of Leinster Gardens – hidden in plain sight. Hardly anyone notices. People live here for years and never see it, but if you are what I think you are, it'll take you less than a minute.

The houses, Mary. Look at the houses.'

What was he doing? She wouldn't see it - why would she see it? John had walked down that road maybe half a dozen times before, when he was doing home visits in the area. He had never spotted it - the missing houses. Why would Mary, his Mary, a simple practice nurse recognise it for what it was? Why would Sherlock think that she would? And clever? he was calling her clever. He rarely called anyone that - certainly not John. Clever was what he admired most in the world. His greatest compliment - why would he pay such a compliment to the person that he thought had shot him?

And then in Mary's voice, an unconscious reflection of Sherlock's own expression when he had worked out something that was - clever.

'Ohhhhh!'

That quickly? She had worked it out that quickly?

'Thirty seconds.' Sherlock sounded impressed too. And John found himself oddly proud of his brilliant wife. How had he not realised? How had he not known that she was that quick, that sharp.

'Because she hid it from you,' came a voice inside his head. 'Because she was concealing from you what she really was.' Cold spread from the base of his neck down his back, his ears ringing so loudly that he could no longer hear the conversation between Sherlock and Mary. His legs felt odd, heavy and lead like and the room in front of him started to swim and fade at the edges even in the dull half-light afforded by the single safety light behind his head.

He was going to pass out and blow all of Sherlock's plans.

Forcing himself to focus, he put his head down on his knees for a moment, concentrating on his breathing, ignoring the conversation going on between Sherlock and Mary. Breathe all the way out, deep breath in, hold it for four, breathe all the way out and repeat. He was hyperventilating, that was all. If he could control his breathing, he could focus, he could stay alert. Sherlock was wrong, of course he was wrong. Mary might not be who he thought she was, but she was still Mary. And he knew her, and loved her and she was intrinsically good. Wasn't she?

The click of the door made him jump and then a figure entered - silhouetted against the light of the street, their face in shadow, but he would have recognised her anywhere.

And she was standing there, staring at him as he sat there. And as much as he wanted to shout and scream at her, to ask her what the hell she was doing, he knew he had to keep his promise to Sherlock. He remained there, motionless, watching his wife who until an hour ago had been one of the two people that he cared for most in the world. And he could say nothing to her at all.

'What do you want, Sherlock?'

'Mary Morstan was stillborn in October 1972. Her gravestone is in Chiswick Cemetery where – five years ago – you acquired her name and date of birth and thereafter her identity,'

Sherlock was saying over the phone, still hidden from view as Mary started to walk slowly down the corridor towards John, believing that the person who was talking was him.

'That's why you don't have friends from before that date.'

Oh God, the wedding, of course. Why hadn't he seen it? No school friends, no cousins, nothing. Who had nobody but a handful of friends and an annoying ex-boyfriend? Somebody who had invented their entire past, that was who.

'You must have an annoying great-aunt or two we need to invite?' he had teased her, but she had just laughed and told him that her family didn't have a good record for living past sixty. Both of her parents had been only children, she had explained, and she had spun the lie so convincingly that he hadn't doubted her explanation for a second. After the car crash that had claimed both of their lives while Mary was in her early twenties, she'd found herself literally alone in the world. Her inheritance was how she had been able to afford the flat, the one that they still lived in. Their home, the one that they were planning to bring their baby home to in a few months time. Oh Christ, the baby. What if she was lying about that too?'

He forced himself to focus. Mary was still walking towards him, still believing he was Sherlock.

'It's an old enough technique, known to the kinds of people who can recognise a skip-code on sight,' Sherlock was saying.

My God, what was she? A spy? Some kind of sleeper sent by Moriarty to reach Sherlock even from before the grave? What was she? This woman who he had taken to his heart and his bed, who had brought him back to life after Sherlock left him empty and broken.

'..have extraordinarily retentive memories ...' Sherlock was saying, and John remembered how Mary could remember the tiniest of details - addresses and entire medical histories of patients, bank account numbers, credit card numbers, every tiny detail of a menu or a holiday. She never got lost, as if she had the entire map of London and every major city stored inside her head. How had he not realised?

'You see what you expect to see, John,' came Sherlock's voice in his head. And so he had.

Mary has stopped now, staring at the man she believed to be Sherlock from halfway down the corridor.

'You were very slow,' she said.

'How good a shot are you?' Sherlock asked conversationally and John had to exercise all of his self-restraint to not duck down behind the chair as his wife, his beautiful wife, pulled a gun from the inside of her coat and he heard the unmistakeable click of the safety catch being taken off. She might struggle to shoot John in cold blood, but she thought that he was Sherlock, and she had already tried to shoot Sherlock once.

'Trust me, John,' came Sherlock's whispered voice in his head. And he did. Against all logic or reason or did, because he knew that however clever Mary, or whoever this woman he was married to might be, Sherlock was cleverer. And he had been here before. He had set a scene, in an abandoned place, with an assassin, and a gun, and he had triumphed before. And he would do so again. Because he was Sherlock Holmes, and Sherlock Holmes always solved the case.

'How badly do you want to find out?'

'If I die here, my body will be found in a building with your face projected on the front of it. Even Scotland Yard could get somewhere with that.'

Of course, a safety net. One that not even Mary could ignore.

She nodded in the gloom of the hallway, but the gun remained by her side. John wondered how quick her reflexes were - if he could shout out in time to alert her to his real identity before she pulled the trigger. Somehow he didn't want to find out.

'I want to know how good you are,' Sherlock was saying. 'Go on. Show me. The doctor's wife must be a little bit bored by now.'

And Mary, his Mary, his wife, reached into her bag, took out a coin, flicked it in the air, and in a feat that the most crack shock in his old artillery regiment would have been proud of, hit it apparently without effort.

My God, who was this woman? And would he be her next target when she realised that he wasn't Sherlock? Sherlock seemed to think that she would care about being unmasked but if she was what he thought she was, if Sherlock had been her target after all, would she just kill them both and disappear?

And then Sherlock was there, silhouetted against the doorway, and John felt relief flooding through him.

'May I see?' Sherlock asked, and he saw the hint of amusement on Mary's face as she realised that she had been tricked How Sherlock must be loving the reveal, his moment of drama. And John almost hated him for that for a moment, for taking pleasure in John's misery.

Mary glanced towards John, and then shook her head, turning to Sherlock with a low laugh.

'It's a dummy,' she said.

'Yes it is,' John thought, 'but not in the way that you think.'

'I suppose it was a fairly obvious trick.'

She walked towards Sherlock and kicked the coin towards him. Sherlock picked it up and examined it.

'And yet, over a distance of six feet, you failed to make a kill shot,' he said, holding the coin up to ensure that John too could see the hole shot straight through the middle of it from over Mary's shoulder.

'Enough to hospitalise me; not enough to kill me,' he continued. 'That wasn't a miss. That was surgery.'

And John realised with a jolt that he was right, that this was what he had wanted to witness for himself, because he wouldn't have believed it any other way. Mary was a crack shot, that much was obvious. If she had wanted to kill Sherlock, then she would have done so. A shot to the head, or even one to the heart would have been easy. She could have killed John too just as easily if that had been her aim.

She hadn't missed. She had shot to incapacitate Sherlock, to give herself time to escape. And yet she had still stayed. Knowing that he had known who she was, what she was. She had still stayed. Why? And over Mary's head, Sherlock gave him the slightest of nods, as if to say 'You know why, John. She stayed for you.'

'I'll take the case,' Sherlock was saying.

'What case?'

'Yours. Why didn't you come to me in the first place? '

'Because John can't ever know that I lied to him. It would break him and I would lose him forever' Thank God, he was right, he was right . It wasn't all lies. She did - did she? Still love him? Was that much at least true?

'And, Sherlock, I will never let that happen.

And then Sherlock was turning as if to walk away from Mary altogether.

'Please understand,' she was saying. 'There is nothing in this world that I would not do to stop that happening.' And for one horrible moment, John thought that she was going to shoot Sherlock after all, and then Sherlock's hand was on the fuse box.

'Sorry, not that obvious a trick,' he said, as the lights came blazing on, and John knew that the time for secrecy was over.

He stood up, wondering what on earth he was going to say to her, as Mary turned to look at him and he saw the realisation in her face. That he knew, that he knew everything. But beyond that he saw something else - not anger, as he might have expected, but fear. Fear of loss, fear of losing him. And he knew that whatever lies she had told, there was one basic truth. She loved him, she was his wife and she loved him and wanted to hold onto him.

But how he felt about her in that moment was almost impossible to determine.

With thanks to Ariane Devere for the transcript of the episode.

If you want to know what happened to Sherlock between leaving hospital and arriving at Leinster Gardens, and specifically how he is still standing and functioning then have a look at Studies in Serotonin, which explores his rationale for the drugs and more.

This chapter comes with thanks to sevenpercent, ThessalyMc and GhyllWyn for the amazing inspiration (and help on plot-holes!) that I have received. You're all fantastic, and you got me writing again. If you haven't read their works on here then you're missing a treat.

Thank you all so much for sticking with this and reading. More soon!

Kate221b