OK I'm going to be completely honest about this fic. It was mostly written before season 4 but following the last three, amazing, roller-coaster episodes I have adapted it to be post season 4. I hope it works and gets us back into the groove of a slow burn case based Sherlolly.

Anyway, I hope you like it.

Chapter 1

There was a serial killer in London and Sherlock couldn't help the frisson of excitement that ran down his spine and settled low in his gut as he contemplated it. He also strongly suspected that at this exact moment, bar the killer, he was the only person that knew and he almost wanted to keep the secret to himself except he knew he shouldn't.

One thing he did know was how much he needed this distraction. Post the whole emotionally wrought episode where he had learnt all about his sister and what she had done it had been a long, boring winter and as Spring had sprung he had been forced to take on cases which in better times he wouldn't have even given a second glance to. He'd even, over Easter, undertaken some work on behalf of his brother; partly to repay him for everything they had gone through together but mostly to give him something to do, anything to exercise his brain and take away that itch that tried to persuade him that one more hit of drugs wouldn't matter. It wasn't that he was particularly bothered for himself but John was still going on about his habit over five months later and he couldn't bear to have it all brought back up again.

Mycroft's case had taken him to the Middle East and he'd had to spend a day perfecting his Arabic before flying out but in the end it had only filled a fortnight of his time rather than the month his brother had promised. Mycroft was getting slow in his old age, missing more; too many cakes and not enough brain work.

But here he was with the evidence of a murder laid out in front of him in his own front room and he knew absolutely that this wasn't the first killing and nor would it be the last. Oh yes he rubbed his hands together in glee, here was a case worth getting dressed for.

Ten minutes later and, following his shower, he was in his room dressing when he heard an exclamation from the front room that had him rolling his eyes.

'Sherlock, these photos, really...'

'Leave them alone Mrs Hudson,' he shouted as he hurried to get back out before she disturbed them.

He was still buttoning up his cuffs as he exited his bedroom to find his landlady placing a tray of tea and toasted muffins onto a corner of the cluttered kitchen table.

He had to admit she did look a little pale after seeing the pictures and he moved forward to help relocate some of his experiments.

'Sherlock,' she remonstrated, 'they're not nice. Why have you got them here?'

'Where else should they be Mrs Hudson?' He said smiling as he took her shoulders and started to guide her out of his flat.

She pursed her lips as she looked back at him, 'you've got a new case haven't you? I can always tell. Well, I'm glad. I don't think my poor walls could have taken much more of your boredom, you'd never know they were newly decorated. Anyway, make sure you eat your breakfast and give my love to Molly.'

This stopped him in his tracks, 'Molly, why Molly?'

Well you'll be going to Barts won't you?'

'Yes, I suppose so,' he said slowly, the confusion clear in his voice. He felt as though there were some clue that he was missing somehow.

'Well then, give Molly my best. She's a lovely girl. You could do a lot worse than her and she likes you. Mind you she won't wait forever; you need to snap her up.'

Once again Sherlock found himself rolling his eyes, it was just Mrs Hudson matchmaking him as ever. At least she'd finally stopped trying to pair him up with John but for a moment there he thought that someone must have told her about that phone call.

Even after all this time he could still hardly bear to even think about it; how he had been forced to say those words to Molly. It had all been thoroughly explained to her by John and backed up by Mycroft and through it all Sherlock had kept quiet. He couldn't explain his feelings to himself so how on earth could he explain them to her. So instead he had said nothing and they had fallen back into their old routines. It was comfortable, familiar and it had been what he needed after finding out about his sister. He hadn't been ready for anything else.

He poured himself some tea and absent-mindedly picked at one of the muffins whilst he went back to his chair. He reviewed the evidence he had so far; three Polaroid photographs and an envelope.

He'd known as soon as it had arrived in the morning post that this was something different. He'd snapped on some latex gloves and held the unopened package up to the light as he'd given it his full attention. The envelope itself was cheap; the sort sold in hundreds of newsagents and stationery shops. His name and address was printed using a home printer, a laser jet, and a stamp had been used rather than a franking machine.

Everything pointed to bland obscurity. Whoever had sent this wanted to give him as few clues as possible. He suspected that when he checked the stamp glue and the envelope seal that they would prove to be moistened with tap water rather than saliva but even that could potentially help him to narrow down a location.

He wasn't too concerned with the postmark on the envelope. It was a London depot but could easily have been posted there to throw him off the scent. No, the real clues came from the photos and yes, Mrs Hudson was right; that did mean a visit to Barts,

As he sat in the cab on his way there he texted John to see if he was available to meet up with him. Between John's new locum work at a local surgery and being a single father to Rosie he hadn't been as available as Sherlock would have liked. That might all change with a new case though.

The cab pulled up in front of the familiar, old hospital and Sherlock quickly handed the driver twenty pounds, waving off the change. He was well known in the local cabbing community as being a good tipper and it was the main reason why there was always a cab available when he hailed one.

His mood was buoyant as he entered the hospital and rose even higher as he made his way down to the morgue where he fully expected to find Molly. This time of the day she was bound to be conducting one of the many autopsies that took place here, and hopefully she would have some free time after to assist him with some tests. He tried to ignore the voice that told him there were more personal reasons why he liked seeing her.

There was so much he wanted to get started with. He glanced at his watch; Lestrade should be here any minute. He almost resented involving Scotland Yard but knew that Greg wouldn't be happy if he had delayed in informing him. He also wanted to get his homeless network in on the thing. But first he needed to give the photograph a full forensic examination.

'Morning Sherlock, have you come to check on your experiments? I don't think there's...oh...what's happened?'

He looked up sharply at the change in her voice, puzzled again at how she always read his mood so easily.

She had paused in her work; goggles on splattered with blood and gore, a circular saw in one hand, the other holding the top of the skull where she had been midway through removing it. She awaited his response looking pensive, a small frown marring her features. He had a sudden urge to use his thumb to smooth out her forehead not wanting to see her worry.

He shook his head slightly, blaming Mrs Hudson for igniting such sentimentality within him. 'We have a body to find Molly. How much longer do you think you'll be?'

She looked down at her unfortunate victim. 'I can be done in about twenty minutes. I'll meet you up in the path lab.'

'Perfect,' he gave her one of his genuine smiles. He tried hard never to be insincere with Molly anymore; she had proved herself to him over and over again and even with all his emotional confusion the one thing he was absolutely certain of when it came to her was that he respected her.

He swung around, making sure to let his coat swirl in the way he knew that she liked, and plunged out through the double doors.

Lestrade arrived in the lab just as Sherlock was pulling on a new pair of latex gloves before he handled the photographs. He didn't think there would be any prints aside from postal workers on the envelope but he had to be thorough, he had to check.

'What have you got for us then Sherlock?' Asked Lestrade as he walked in with a grumpy looking Donovan trailing behind him.

Sherlock's eyes flicked over to them, taking in all those small clues that other people just didn't seem to see, the dirt on Greg's trousers which told him he'd taken the tube into work, the outfit which told him Donovan was going for an interview that day and was nervous about it, checking her watch twice already in less than a couple of minutes. At least she had stopped calling him freak since he'd been exonerated of all Moriarty's accusations though she'd never gone so far as to apologise to him. He knew she still didn't like him but he didn't care about that.

He gestured to the items he was laying out in front of him. As Lestrade and Donovan came over to look he described how they had arrived in the post that morning.

'Fucking hell Sherlock!' Was the sole, initial response from the Detective Inspector with a long low whistle from Donovan.

'Well, there's no doubting she's dead, any idea as to where or when this might have happened? Is this a recent murder or just evidence of something historic?'

Sherlock pointed to a paper, just visible in the top right of one of the photos, and he passed over his small retractable magnifying glass, 'Sunday's paper, going by the headlines, so the pictures are less than 72 hours old. I need Molly to confirm it but the body looks fairly fresh to me, so it looks as if the murder took place on or around the same time.'

He continued, 'she looks to be about twenty to twenty two, working as a prostitute though in the poorer end of the market. Her clothes, what remains of them, are cheap, mass produced. Her fingernails are unkempt, long term nail biter, no manicure which is unusual nowadays. I'd say she was new to the trade, maybe a runaway or someone who moved to London with aspirations which quickly faded.'

Lestrade wiped a hand over his face and turned away. 'Fine, we can check our lists and see if anyone matches the description. Don't suppose you know where the killer will dump the body?'

'Probably the Thames. He's clever, he's done this before and he'll know that the water will eradicate a lot of the evidence. We need to cross-reference any similar, unsolved murders. This isn't the first time he's killed.'

Lestrade shook his head and took a deep breath. He spoke at the same time as Sherlock, their voices overlapping, 'I hate serial killers!' 'Serial killers, I love a good serial killer!' Sherlock clapped his gloved hands together with glee and turned back to work on his tests oblivious to the look of disbelief which passed between Lestrade and Donovan as they made their way out of the lab.

Twenty minutes later and bang on time Molly joined him, bringing with her two cups of coffee. She set his down on his right and observed him whilst she sipped on her own. He could almost feel her eyes travelling over his body, as they always did, and just like always he ignored it. He knew how she felt about him, after that phone call it couldn't be ignored, and he knew she found him physically appealing but it was irrelevant, all aspects of sex were irrelevant. It was the mind that mattered, the rest was just transport.

He sighed a little, it didn't matter how many times he repeated that line to himself it didn't seem to make it a truth any easier to bear or believe.

Within a couple of seconds she moved over to view the photos of the dead girl. 'So this is your latest case then? No body yet?'

He finally looked up meeting her eye. 'Yes and no, the photos came in the post. I've checked for fingerprints but unsurprising there aren't any; now I'm checking the envelope glue and stamp for any liquid residue. It's too much to hope for any saliva but tap water would at least help us to place the killer if not the crimes.'

Molly put down her cup. 'So, how can I help?'

'I need you to review the photographs, tell me what you can about the injuries, mode of death, time since death. Anything you can.'

He couldn't help but feel a swell of emotion at the companionship he felt with her as between them they set to work.

So Sherlock is ignoring the obvious and trying to pretend his feelings didn't happen. Well, we can't make it too easy can we...I still love a slow burn :)