'Don't tell me - you're not angry with me, you're disappointed in me?'

'Nope. I'm absolutely fucking furious with you.' John shook his head at Sherlock's expression, moved away and slammed his fist into the wall of the living room in 221b, leaving a slight dent in the plaster under the wallpaper, that would have Mrs Hudson wringing her hands in horror. But it was better than his preferred option of making an even bigger dent in the soft tissues of Sherlock's face.

'John-'

'What?' John yelled, not caring that Mrs Hudson was downstairs and could probably hear every word. 'What can you possibly say to make this better, Sherlock? You lied to me. You've been using drugs. A whole bloody cornucopia of the stuff. Enough drugs to make the average junkie roll over with his legs in the air. What the fuck were you thinking?'

'You know what? I don't even want to hear your explanations. But you know what pisses me off the most? You lied to me. Over and over again you lied to me. And I thought -' his voice caught and he sat down with a thump in the armchair - his armchair. 'I just thought that you respected me more than that.'

'It was necessary.'

Sherlock's voice sounded vague as he moved to the window, lifted the curtain and stared out into Baker Street, eyes narrowed as if trying to calculate a tricky equation.

'Necessary? What could require you nearly killing yourself? Just tell me that.'

'I needed answers and I needed them quickly. My Mind Palace was the only way to do that.'

'And your Mind Palace requires drugs to access it? Is that what you're telling me?'

Sherlock turned back to him. 'I've disappointed you, John,' he said, without any trace of emotion in his voice.

'Disappointed me? I'm not your father, Sherlock. I'm not even your brother.'

'No, you're not.'

'So what - I have no right to ask you to hold yourself to a higher moral standard than you appear to want to do?'

'What did you say?'

'I said, that it's probably unreasonable for me to expect you to act like a sensible member of the human race.'

'No, you didn't.' Sherlock frowned slightly, staring at John. 'You said that you expected me to hold myself to a higher moral standard. That's what you said in my mind palace too.'

'So I was in your mind palace? Am I supposed to be flattered by that?'

'Oh, it wasn't just you. Mycroft was there too - and Lestrade. Mary, Molly Hooper, even Anderson put in a brief appearance.'

'And what? We were all involved in your lovely little trip to work out a hundred year old, unsolved case.'

'An important case, John.'

John shook his head in disbelief. 'I don't get you. I really don't. Look I'm trying to be understanding here, but don't you have the tiniest bit of insight into the fact that taking drugs in order to solve a case is the most deluded, self-destructive IDIOCY that I have ever – EVER- come across. You stupid, stupid - bastard.' John realised that he was shouting and forced himself to stop and take a deep breath, struggling to get his anger under control.

'Why does it bother you so much?' Sherlock asked.

'What?' John stared at him, trying to work out if he was being sarcastic,

'Why should it bother you that I took drugs to access my Mind Palace? Why did it bother you when you thought that I was taking them before, when you found me in that squat? Why does it matter how I do what I do? Moriarty could have been back. I had to -'

'You had to what? Kill yourself? Because you can't admit that you don't have all the answers?' John was standing up now, fighting very hard the urge to walk over and punch Sherlock in his smug face.

'Five minutes previously, I thought that I was going to go off and allow myself to be killed in Eastern Europe. My chances of survival in the Mind Palace were significantly higher.'

'What on earth are you talking about?''

'It was a one-way mission. That was the point. Didn't Mycroft tell you?'

'He implied that it was dangerous, but the words 'one-way mission' certainly weren't used. I would have noticed.'

'It was a suicide mission, John.'

'But you would have still have had a chance.'

'And I had a chance with the drugs. The possibility of a fatal overdose was low, and besides which I knew I would be back on the ground within ten minutes. The need for medical attention would have been inconvenient, admittedly, but it was worth the risk.'

'Christ, have you listened to yourself?' John interrupted him. 'Sherlock you have a drug problem. Why can't you see that? It's not normal to use drugs to help you work. It's not normal for your brother to find you unconscious in a drug den or an alley or God knows where on multiple occasions. It's not normal - '

'And is that what I should want to be? Normal?'

John recognised the defensive look on Sherlock's face and decided that it was time to change tack. 'Sherlock, come on, this is the addict in you talking. You're out of control and you know it. Look I know a good drug and alcohol counsellor. I could get you an appointment tomorrow - maybe even this afternoon. Won't you at least go and talk to her.'

'No time, John,' came the reply as Sherlock marched over to his laptop and flicked it open. 'We've got work to do.'

'Work to do?' John repeated.

'Work, yes, Moriarty is back, remember? Or rather he is not back but somebody is creating the illusion that he is back; using his image, his memory to create chaos. And the question is - why?' Sherlock's eyes gleamed with the excitement of a new case, a new challenge.

'And will you be using drugs to help you get these answers?'

'If I have to, yes.' There was the light of challenge in Sherlock's face and John had learnt better than to try to argue with him in this mood.

'Then count me out.'

'What?'

'You heard me, Sherlock. Count me out. Because if you think that I'm willing to just sit here and watch you justify snorting, or whatever you do with those drugs, yourself into illumination then you're wrong. I won't do that.' John stood up and grabbing his coat from the back of the door, shrugged it on.

'You're asking me to make a choice.'

'Give the man a prize. Yes, Sherlock, I'm asking you to choose. Me, or the drugs. You're going to have to decide which one of us you need to work more. Because I won't stand by and watch you destroy yourself with this. I can't. Don't you understand? After all that you've put me through in the last few years, do you honestly think that I'm going to stand by and watch you do this?

'When you're ready to admit that you've got a problem, then give me a call. Until then, you're on your own.'

...

John walked down Baker Street shoulders hunched, muttering to himself, but instead of heading for the tube and home, he headed instead for Regent's Park. He needed some time to cool off before he faced the jostling mass of people on the tube. In the mood that he was in at the moment, he might just thump anyone who looked at him the wrong way. Bloody Sherlock, why couldn't he admit that he had a problem? Why couldn't he see what he was doing to himself?

He turned left inside the gates of the park, skirting round the outside of the boating lake rather than facing the more popular walk towards the rose gardens and the outdoor theatre. By the time that he had reached the far end and crossed over the bridge, he had calmed down a little, and stopped at the kiosk to buy a coffee. As he poured in the white granulated sugar from the sachets and gave it a stir with the wooden stick provided, he found himself wondering if this could have been how Sherlock had been getting the drugs into his system. Cocaine in his coffee? Amphetamines in his tea? Surely not, but then how? How had he been taking them when John had been staying at 221b with him for much of the time since his discharge from hospital without him noticing? 'You see, but do not observe, John.' Had it been right in front of his eyes the entire time?

The realisation of his own failure threatened to reverse all of the benefits of his walk and the physical distance that he had been trying to create between himself and an impossible situation. Forcing himself to acknowledge that anger was going to get him nowhere, he turned instead to the techniques learnt in his months of counselling after his return from Afghanistan. Trying to take a step back, and work out why he was so angry.

'You can't always change a situation, but you can often change how you feel about a situation, and that, in turn, will change how you react to it,' came Ella's voice.

He was angry with Sherlock because he had been using drugs. Because John himself could not understand how somebody so brilliant could feel the need to pour that junk into his body just to prove that he was more clever than anybody else.

And then he understood. It wasn't that Sherlock wanted to be cleverer than everybody else. It was that he needed to be cleverer than everybody else. Because if he wasn't, then what did he have?

And he believed that the drugs were what made him like that. How long he has been using the drugs for, John had no idea. He remembered Sherlock entering his Mind Palace in Baskerville, and he remembered him using the technique before that - to sort data, to recover memories, to solve cases, Had all of that been drug-fuelled?

He remembered Sherlock's words on Bart's roof, and wondered how many of them had been true. 'It was a trick. Just a magic trick. I discovered everything that I could to impress you.'

Had the trick been drugs all this time? He didn't believe it, not for a second, but if Sherlock believed it, then...

Then he was asking Sherlock to give up the one thing that he cared about. 'It's all about the work.' How many times had John heard him say that? And 'The mind is what matters. Everything else is transport.' And if John was asking him to give up drugs, would that in his mind mean giving up the work? And if he was giving up the work, then -'

And then John realised what he had done. And he turned back towards Baker Street, walking as fast as he could and then breaking into a run when even that proved too slow.

'You can't blackmail an addict into stopping using,' he remembered the peer support worker telling him during his short stint with the Drug and Alcohol Team as a GP Trainee. 'You can't plead with them to stop in order to prove that they care about you. It doesn't work like that. In their head, all that they have, all that they are is based on their habit. And if you take away that, then they believe that they have nothing. If you withdraw your love and support then they will only turn further to the drugs, and if you take it away entirely, then they may lose hope altogether.'

'But if you don't say anything, then aren't you just condoning their actions?' he had argued, thinking of Harry. Thinking about how he could never bear to just sit there and watch her drink herself into oblivion. About how eventually always crack and tip the contents of every bottle of alcohol that he could find down the sink. But there were always more. Somehow, she always got hold of more.

But the peer supporter had just shaken her head at him. 'You're missing the point,' she had said. 'It's all about control. The majority of addicts use to escape themselves because they feel somehow damaged, incomplete. The only person who can make an addict stop using is themselves. Try to take the control of their use away from them and what do they have left? You risk leaving them with only one possible option. And that is why the time when an addict is facing up to their illness is the most dangerous time in terms of overdose.'

John knew that, he knew all of it, he had just dragged it out of his long-term memory in a feat that even Sherlock would be proud of. So what sort of useless doctor was he to allow his anger to override his concern for Sherlock?

Sherlock hadn't done this to piss John off. He had done it because he was an addict. He hadn't hidden his habit from John to be devious, he had done it because that was what addicts did. And he wasn't refusing to accept that he had a problem to be difficult, he was doing it because he had a deep and entrenched addiction and was terrified of facing life without a pharmaceutical cushion.

And John should have known all of that, but instead, he had treated him like a five-year-old and abandoned him. And knowing Sherlock, and how he reacted to being backed into a corner, there was only one possible outcome to that.

It took him a less than fifteen minutes to get back to Baker Street, and when his knocking went unanswered, he lost no time in letting himself in at the street door. He ran up the stairs, and entered the flat without knocking, panting with the exertion of the run.

'Sherlock, I'm sorry,' he said. 'I didn't get it. I do now. I know it's not that easy, I know you can't just -' and then he stopped talking as he walked round his chair and saw the syringe lying on the floor, and next to it the prostate, barely breathing figure of Sherlock Holmes.

This started life as a 'five plus one' story and got by far the most votes to be continued.

There are four chapters of this in total - hope it was worth the wait. This is for everyone who read the original 'Explanations' and who voted. If you didn't get your choice, then feel free to PM me - I'm always open to persuasion!