'Has he been messaging you too?' John asked as he returned to the table with two fresh pints of Adnams to see Greg shaking his head at his mobile phone.

'He just can't leave it alone can he? Irritating bastard. He says I'm to make sure I tell you everything.'

'What's this all about, Greg? Do you know? Why now?'

'Honestly? I think that he's scared, John.'

'Scared? Sherlock? He hardly ever gets scared. Horrified that he's been outwitted, yes, but few people other than Moriarty have ever really got to him.'

Greg shook his head. 'You didn't know him before,' he said. 'By the time that you came along he'd sorted himself out, cleaned himself up, got off the drugs and was making a reputation for himself. If you'd seen him a year before that, you'd understand why he's scared. If he's slipped and is seriously using again, then we're all in for a hell of a ride.'

'How many times has he been through detox and rehab?'

'At least three that I know of - that's offficially. I suspect at least twice that number on his own.'

'Why does he never talk about it?'

'I imagine that he's 'deleted it' from that memory of his. That's what he seems to do with a lot of uncomfortable stuff.'

'So why hasn't he deleted Christoph?'

'Maybe the memories weren't entirely bad.'

'Do you think that -'

'That he loved him? I'm sure that he did, John.'

'What can you tell me about him?' John asked. Wondering why he was desperate for details. 'Why did Sherlock care so much about him, do you know? Why him?'

'Christoph was a year older,' Greg explained. 'He was different, he spoke a different language. He and Sherlock conversed almost entirely in French did you know that? He'd taught him fluent French within a couple of weeks, imagine that,' Greg shook his head. 'It's as much as I can do to ask for steak and chips.'

'Did he speak it at all before that?' John asked, fascinated.

'Schoolboy French he told me, and a couple of holidays in France but that was it. Turns out that when they met, Christoph's English was worse than Sherlock's French, so they went for the simplest communication option.'

'He would have liked the challenge of that.'

'I'm sure that he did.'

'So what happened to him, did you find out?'

'That first day, I ended up going to the warehouse to investigate myself, with one of the juniors. Sherlock was right. There were bloodstains there and signs of a struggle. Looked as if the kid had been tied to a chair and beaten bloody. There was a mattress in the corner, with blood and goodness knows what all over it. Forensics indicated they'd raped him once he was too out of it to resist.'

'And then they killed him? Why?'

'It was part of the pattern, John. Christoph wasn't the first.'

'Jesus, you mean it was - what - a serial killer?'

'More of a paedophile ring whose tastes ran to the sadistic. Christoph was the oldest of the boys that they took.'

'How many?' John asked, trying to force down the urge to vomit.'

'Four - that we knew of. Sherlock helped us nail the bastards. We secured convictions for rape and murder for three of the men, four others with various conspiracy to assist and paedophile charges.'

'For what?'

Greg pulled a face. 'They liked to watch,' he explained.

John closed his eyes and turned his head away for several minutes, trying to work out if he was going to have to make a dash to the Gents to vomit after all. Eventually he took a sip of his beer, then another. It helped.'

'You okay?' Greg asked.

'Not really, no.'

'For what it's worth, it's probably the most vile investigation I've ever been involved in.'

'And Sherlock nearly became victim number four. No wonder he became obsessed with murders.'

'It's worse than that, John. He nearly became victim number five. He tried to set himself up as bait.'

'Of course he would, the stupid bastard,' John murmured. 'How did you stop him?'

'Fortunately I found him before they did, worked out what he was up to. Arrested him, threatened to charge him with soliciting and possession with intent to supply unless he told me what the hell he was up to.'

'And?'

'And when we searched him at the nick we discovered that he'd rigged himself up with a fairly sophisticated recording device, programmed to broadcast any sounds in the vicinity onto the police network with the touch of a button. It also contained a tracking device to ensure that we would find him.'

'So what was he planning to do?

'As soon as he was picked up, he was going to activate the device, it and do his damnedest get us all of the information that we needed to convict every single person in that gang.'

'But how did he know you'd find him in time?'

'He didn't, John. That's was the point. He was going to sacrifice himself to catch Christoph's killers and he was furious when we prevented him from doing just that.'

John paused to consider. So this martyrdom complex, this willingness to sacrifice himself for those he cared about and for the greater good wasn't new. And yet it seemed to run so contrary to Sherlock's general unawareness of the emotions of others on a day to day basis.

'Not others,' said a voice in his head. 'Just strangers. He cares if he upsets you - or Molly, or even Mrs Hudson. He does care, he just lacks the emotional intelligence to work out the consequences of his actions before he's carried them out.'

'So did you charge him?' he asked Lestrade.

'No. He didn't have enough on him to charge him with more than possession, and we cautioned him for that. Besides, I felt sorry for the kid. We got him a shower and some clean clothes and I found him a bed in a hostel for a few nights. Told him if he could keep himself straight for a few days then he could help us. Then I went back to the nick and started trying to work out who he was.'

'Couldn't have been many Sherlock Holmes on the missing persons list, surely?

'Well that was the problem. He wasn't listed as Sherlock, he was listed as William, known as Will, because that was what his parents called him in those days. And he hadn't given us his surname. I had a flick through the database but there were hundreds of teenage runaways on there, and before the days of digital cameras it was all bad photocopies and dodgy school photos. Sherlock had short hair in the picture that his parents had provided. He'd been on the streets for nearly six months by the time I met him and he'd changed almost beyond recognition from living unde those conditions.'

'But he'd left us a big clue. The transmitter he'd wired himself up to was state of the art. Not the sort of thing you could pick up on the street, and the Internet hardly existed in those days. I had it analysed - took ten days for the results to come back, turns out it was security service issue and they'd rather like it back please.'

'So how - Mycroft?' John asked.

'Precisely. Turns out Sherlock had broken into his big brothers flat to help himself to some cash and found that in the process. Mycroft was in the early days of his training back then. Got into a ton of flak for leaving equipment lying around until Sherlock later admitted he'd taken it out of Mycroft's safe after cracking the code. After that they tried to recruit him to GCHQ, but of course he was having none of it.'

'So how did that help you work out who he was?'

'I made discreet enquiries about if any of the agents had a teenager relative who'd gone missing. It was a long shot but it worked. A week later, Mycroft Holmes phoned me to arrange a meeting with and brought with him a picture of Sherlock.

'And you recognised him?'

'I couldn't be sure, but there was something about Mycroft that reminded me of him -an imperiousness, I suppose. Then Mycroft started telling me about Sherlock and the more he told me, the more I was sure he was talking about the same person.'

'And they had a happy reunion?'

'Of course not. Sherlock had left the hostel before we got there. Didn't track him down for three weeks and then he was found unconscious under a bridge. He'd overdosed. But at least we knew who to call.'

'And the case?'

'Was solved by then. Turned out Sherlock had worked out where two of the other boys had been picked up from but hadn't chosen to share the information with us because he knew I'd stop him using himself as bait. Correctly as it turned out. Even back then he'd realised that people would tell him things they wouldn't tell us. Based on the information he got from the other street kids, he worked out that the gang had tried it on with lots of other boys, but they'd got spooked. He worked out where they were hunting, the colour and probable make of the van they used, everything.'

'Why didn't he just tell you?'

'Didn't trust us,' Greg said. 'He was an arrogant sod, even back then. Reckoned he could do a better job himself. The information that he gave us enabled us to track them down after he did his disappearing act.'

'So that was how you met Sherlock,' John said, surprised to discover that his pint glass was almost empty again.

'That was how I met Sherlock,' Lestrade agreed. 'You can see why he's not keen on me sharing that story. Not with most people, anyway. But then you're not most people.'

'How do we get through to him, Greg?' John asked. 'How do we get him to stop using?'

Greg looked puzzled. 'You can't,' he said. 'You know that. You've worked with enough addicts in your time, you must have. Only Sherlock can stop Sherlock using. All we can do is support him.'

'I want to shake him by the scruff of the neck and send him off to a remote Hebridean island where there are no drugs in sight,' John said.

'Won't work,' Greg said with a grin. 'I tried it. The shaking that is. Many times. Shaking, shouting, threatening with arrest. None of it works. He'll stop when he decides he wants to, and when he does, he'll just do it. Oh, I'm not saying that it will be easy, or that he won't slip a few times along the way, but he'll do it and he'll be clean for months or years and then the cycle will start all over again.'

'So how do you break the cycle?'

'Well you can't, can you?' Greg said. 'He's an addict, John. He'll always be an addict. The cases, they were a way to distract him, they give him a different kind of fix, but he's always looking for the high, always will be. I don't think you can change that.'

'So what - I shouldn't try?'

'You shouldn't feel responsible, John,' Greg said, standing up and picking up the empty pint glasses. 'He's an adult. He can look after himself. Well most of the time. He'll do it when he's good and ready, as I say. Now how about another pint and something to eat? They do a good burger here.'

John nodded and pulled out his phone to check his messages as Greg headed towards the bar.

Well? SH

I think that I understand now JW

Astound me SH

It was the beginning of it all JW

Don't pity me John SH

I wouldn't dream of it JW

And then - radio silence. No more messages.

Greg returned with the beer and the menus, they ordered food and spent the rest of the evening doing what two men do in a pub - drinking, eating and talking about anything and everything as long as it didn't involve emotions or the nearly impossible task that they had in front of them.

And that's it. For now. If you'd like more then do please let me know. I'm always open to pleas. And to bribery and corruption of course

This story is for everyone who read and commented on the original Explanations series - your enthusiasm is what inspired me to keep going with this one. Thank you so much for all of your fantastic feedback.

Thanks as ever go to my amazing beta team if BaillierJ and seven percent for helping me iron out the creases.

And if you like medical realism / grit and John getting to be BAMF Dr Watson then you might like to have a look at the 'BAMF Dr John Watson #medicsl grit' (I know, sorry. I couldn't resist) community that BallierJ and I have set up. Suggestions for that also gratefully received.