It's a particularly good day for Sherlock. He'd managed to avoid Mycroft's surveillance team (idiots who hadn't thought to look up when he disappeared down an alleyway) and he'd even found a new dealer. The old ones had all been scared off by Mycroft. Honestly, it was like they were ignorant to the fact that dealing drugs was illegal until one of Mycroft's minions informed them. It was worse than that, though because whoever was sent would threaten prison time only if they sold to Sherlock again. He was getting a bit of a reputation around dealers; it made them nervous to sell to him. They were waiting for a black car to roll up to them on the street as had happened to so many of his previous dealers. As far as Sherlock was concerned, they were all idiots anyway. They just happened to be idiots who had what he wanted, making them (unfortunately) necessary idiots.
The new dealer hadn't been warned about him, yet. Sherlock collapsed onto a couch (was it his couch? He dismissed that as irrelevant) in a blissful haze. Finally, he could get some measure of quiet as his mind was as silent as it could get. He loved his mind and prized the knowledge he possessed but knowing everything about anyone and anything he happened to glance at could get tiring. Not that he was overwhelmed - he trained his mind far too vigorously to ever feel overstimulated by his knowledge, and his memory palace, if he said so himself, was magnificent. Sometimes, peace was all he craved, though. Knowing all that he did and the ease of finding out what he didn't made life too easy. Made it boring. And he hated being bored.
Being high dulled him enough to still be leagues higher in terms of intellect and observation than his peers, but made him have to work harder, think more to reach his normal levels of intelligence. It was refreshing. He didn't do it often, but just enough that it had become a habit. Sherlock knew he wasn't addicted, no matter what Mycroft thought, or the signals that his body gave when he was going through withdrawals. His mind was untouched by addiction, only his body was - he could stop any time he wanted to. He just didn't want to. Sherlock's body did not rule his mind, so no matter what his body was telling him, that it craved the drugs, or food, or sleep, if he didn't want it, he didn't do it.
Mycroft wasn't the only person to worry unnecessarily about him. Detective Lestrade worried when he turned up at crime scenes that he wasn't invited to. Granted, Sherlock did look a bit worse for wear sometimes, but that was to be expected. His mind worked at levels too high for them to comprehend so he neglected the more mundane activities that other people thought were necessary. At least once a month Lestrade would comment that he was looking a bit thin, or a bit cold. He nagged more than Mummy did. Mummy, thankfully was unaware of his drug-taking habit, so he got to avoid the nagging and lectures she'd surely unleash on him if she knew. She wouldn't understand why he did it anyway.
The only person who came close to understanding was Mycroft but even he didn't fully get it; something Sherlock was sure irritated his older brother beyond words. If the roles were reversed Sherlock would likely feel the same - not knowing, not understanding was an antithesis of the Holmes brothers. There was only one person who understood Sherlock's reasons, and he was fairly sure that she was a hallucination provided by his drug-addled mind. The person who understood him was a little girl with frizzy hair and a wide grin who wandered in and out of his life when he was high. There was a high likelihood that she was real - some random girl he had seen walking the streets somewhere that he had deleted the origin of. She didn't even have a name but she was cherished. She had her own room in Sherlock's mind palace and could often be found skipping down the cold corridors cheerfully. Although he was aware that this girl was a stranger and was not even real to him, he still closely guarded their interactions. She was always friendly and amazed by his intellect rather than being disgusted or turning away from him. She cared for him, he thought. She comforted him when he needed it - rather like Redbeard.
She encouraged him to do better, to make something of his mind. She called it a blessing. Told him to do something worthwhile with it. She told him that if he could challenge himself, then his mind would be quieter without the need for the drugs.
He had tried to take her advice and had started to conduct experiments. It wasn't enough. He needed something more. She was the one who had suggested solving mysteries, so he moved on to famous cold cases but quickly found them frustrating because of the lack of evidence. He was brilliant and he was a Holmes but even Sherlock couldn't pull an accurate solution out of his arse with nothing to suggest it. Something fresher was needed to keep him occupied. Crimes scenes were the girl's suggestion. Sherlock was surprised when it worked and kept him busy and his mind quiet. He wasn't there to make friends so he wasn't shocked to find that he was unwelcome at the crime scenes he attended.
Sherlock had cultivated a relationship with Lestrade, who called him when the police had hit a dead-end, or when he thought Sherlock was looking a bit manic, a bit like he was looking for his next hit. It was intriguing work, sometimes but he often found it to be so elementary that he wondered if Lestrade and his team had a working brain at all. As jealously guarded as the girl was, it had helped him to talk to her about his case, the clues, to mull it over with her. She rarely said anything but worked as an adequate sounding board.
However, Scotland Yard already thought he was insane and talking out loud to a girl who lived in his brain would only cement that reputation. He decided to get a flatmate. None of his flatmates stayed long, usually saying that Sherlock was too difficult to live with. They didn't suit Sherlock's purposes, anyway. None of them wanted to hear about his cases, none of them wanted to be a sounding board for him to expunge his deductions and thought processes on. He bought a skull and named it Billy instead. It turned out to be much more useful than any of his flatmates had ever been.
Along with attending crime scenes and requests from Lestrade, Sherlock decided to start taking private cases, too. He set up his website and it was largely useless but there were occasional tips about interesting cases. Sherlock suspected that they were mostly, if not fully, from his brother in an attempt to keep him busy. There were plenty of tips about cases that were just plain boring. Mostly people wanting to know if their partner was cheating and other such trivial things.
His job title was too vague, he realised. Most people seemed to think he was a private detective, who would be happy to find lost items or cheating spouses for them. He was not. He was something else - something unique. He needed a job title as unique as his services were. Sherlock had listed a few but none seemed to fit (deductor? Sounded like a comic book hero - no. Investigator? Far too wide and too similar to a private investigator - he did not need any more confusion about the services he offered).
Sherlock decided on consulting detective.
He was a consultant, sort of, to New Scotland Yard, and if he had wanted to go into the police force he supposed he would be most content as a detective. It made sense so he updated his website with his new job title. The next time he saw the girl she was beaming proudly at him. He pretended he didn't see it.