In her lab at Barts, Molly Hooper is sitting at one of the workbenches. She's already put on her jacket, ready to leave for the day, and her bag is next to her on the bench. Outside the windows, it's already dark. Molly distractedly turns the pages of a medical journal, but more often than not glances instead at her phone that lies close at hand, as if waiting for a call.

Then the door bursts open, and Greg Lestrade, Sally Donovan and Sherlock come practically storming into the room. They seem to have stopped over at Baker Street on their way here for dry clothes for Sherlock, but he still looks a little dishevelled. He's probably had to change in the car.

LESTRADE (to Molly, urgently): Has he called you yet? The man you've been chatting with?

Molly doesn't seem very surprised, neither at their sudden appearance nor at the question.

MOLLY: Yeah, about half an hour ago. (She produces a piece of notepaper with a mobile phone number jotted down on it from her bag, and hands it to Lestrade.) That's the number he's using.

Lestrade baulks at her calm, collected tone.

MOLLY (a little puzzled): Sorry, did I do wrong?

Lestrade opens his mouth, but Sherlock – who seems less surprised than Lestrade, but even more alarmed - is faster.

SHERLOCK (to Molly): Are you meeting him?

MOLLY (with a small smile): Right now.

SHERLOCK (rather brusquely): Where exactly?

MOLLY: Camden Lock, as arranged. (Frowning at Sherlock's tone) I thought you'd all be there already, I didn't -

Sherlock instantly whips around to Lestrade.

SHERLOCK: You heard that. Let's get going.

LESTRADE (still at a loss): What?

SHERLOCK (herding Lestrade hastily back out of the door): Come on! Or do you want to find him drowned?

Lestrade exchanges a puzzled look with Sally Donovan, but then they let themselves be swept along, leaving Molly behind in now equal confusion. But just when the door is about to fall closed behind the three others, Molly grabs her bag from the workbench and sprints after them.

MOLLY: Wait! I'm coming with you!

Camden Lock. Night time. The picturesque banks of the Regent's Canal, always teeming with shoppers and tourists in the daytime, are empty in the darkness . The willow trees on either side of the water loom black and massive, casting the waterside into deep shadow. There is no activity at the twin lock on the canal that gave the area its name, and the towpath that runs alongside it seems deserted. From the surrounding brick buildings - warehouses and stables now converted into fashionable shops and cafés - only an occasional snatch of laughter or conversation comes floating down to the path, when a door opens and closes. Cars and buses are going past on the nearby Camden High Street, but their lights don't reach down here. The water, sluggish and with patches of duckweed floating on its surface, looks pitch black.

A solitary man stands on the northern bank of the canal, near where a brick archway gives access to the Camden Market area. He has his phone out, obviously just whiling away the time while waiting for someone. In the faint light from the screen, he can be seen to be in his thirties, with altogether unremarkable short brown hair, and dressed equally unobtrusively in a dark jacket and jeans. His face is roundish, with smooth cheeks and slightly hooded eyes, and he wears a scarf high around his neck.

Then from the direction of the lock, another man approaches, treading silently, no more than a shadow in the darkness. He halts a few steps away from the archway, and addresses the man standing by it - in John Watson's voice.

JOHN (quietly): Oliver?

The man with the phone looks up in surprise, squinting into the darkness to make out who's talking.

MAN: Yes?

JOHN: Or is it John? Or Henry? Or George?

The stranger has spotted his opponent now. He quickly slides the phone into his pocket.

MAN (alarmed): Who are you? Are you the police?

JOHN: Interesting question. Why would I be?

MAN (quickly): No reason. (In a tone of forced calm) Look, I don't know what you want, but - (He gestures behind him, in the direction of the archway.) - but I'm meeting someone, so…

He begins to retreat towards the archway leading into the market area. John quickly steps out of the shadow of the wall to let his face be seen.

JOHN: Yes. You're meeting me.

He reaches behind him, and when his hand comes up again, he's holding his gun. He raises it to point directly at the stranger's head. The man's jaw drops, and his expression turns into a grimace of sheer panic.

MAN (in an incredulous stammer): But - but you're the doctor!

JOHN: Yes. And your treatment isn't over yet.

Camden Lock. Night time. Greg Lestrade's car comes racing up Camden High Street in complete defiance of all speed limits. With screeching tyres, it halts at the kerb just south of the road bridge across the canal, and four people tumble out of it - Greg Lestrade himself, Sally Donovan, Sherlock and Molly Hooper. They immediately set off along the narrow walkway that leads past a closed coffee shop down to the waterside on the southern bank, until they're level with the lock. At the low iron fence separating the public footpath from the operating area of the lock itself, Sherlock halts, and holds up his hand to demand silence. They listen intently for a moment, and there it is - the sound of splashing water, and feeble whimpers of pain or protest, a little further up the canal.

MOLLY (pointing across at the willow tree overhanging the northern bank): Over there!

Lestrade and Sally Donovan immediately set out towards a footbridge that spans the canal twenty yards further on. Sherlock hesitates, but then instead of following them, he swings himself over the fence right into the lock area itself. A single long step takes him from the bank onto the narrow upper edge of nearest sluice gate. Using it as a balance beam, he makes his way across the water at break-neck speed, arms held out on either side like some demented tightrope-walker. Molly Hooper, who has remained behind on the southern bank, claps her hand to her mouth in alarm. Sherlock teeters precariously once or twice, but he safely reaches the other side a valuable half-minute before Lestrade and Sally have negotiated the footbridge.

In the distance, the sirens of several police cars can be heard approaching, and a moment later, their flashing blue lights have appeared on the road bridge. Molly, who has remained behind on the southern bank of the canal, looks around, quickly makes up her mind, and runs back towards the road to meet the reinforcements and show them where to go.

On the northern bank, Sherlock is the first to arrive at a short flight of stone steps that lead down from the towpath onto a small wooden landing stage right at the edge of the water, a little beyond the archway into Camden Market, hidden from sight underneath the hanging branches of the willow.

Two figures are crouched on it, one above the other in an ungainly heap. The one at the bottom is on his knees, his head and shoulders down at water level, while the one on top has his hand on the back of his victim's head, and keeps ducking it in the muddy canal, holding him under for a few seconds before letting him up again.

SHERLOCK (shouting at the top of his voice as he comes slithering down the damp steps): John! Stop it!

He reaches the landing stage. The thump as his weight lands on it makes the man on top – John, indeed - pause and look up. A moment later, Sherlock has already wrapped his arms around his friend, and is hauling him bodily off his victim.

SHERLOCK (still shouting): Stop that, you idiot! D'you want to kill him?

Lestrade and Sally Donovan arrive. Seeing John taken care of, they immediately make for the other man, who has collapsed on the landing stage, wheezing and spluttering, his upper body wet through and through.

John twists out of Sherlock's hold, but once freed, he only straightens up and calmly rearranges his clothes. He no longer deigns to even look at the other man, who is being pulled into a sitting position by the two police officers, clearly alive but too weak to protest or resist. John gives Sherlock a rather reproachful look, then reaches past him for his phone, which is sitting propped up on a narrow ledge in the stone wall of the canal. John switches it off, and hands it to Greg Lestrade.

JOHN: That's the full story on there. Just in case he'll have trouble remembering any of it once he's talked to a lawyer. And you might want to send someone to trawl the pond on Peckham Rye Common straight away. Another day in the water probably won't improve the state of the laptop, the phone and the towel he dumped in there.

Lestrade, astonished, takes the phone from John without a word.

JOHN (with a crooked smile): And now I could do with something to warm me up.

Gathering his dignity about him, he turns away and starts climbing the stairs back up to the footpath - just as Molly Hooper, with a team of uniformed policemen in tow, finally comes hurrying towards them from the direction of the road.

The coffee shop on the corner of Camden High Street, between the main road and the lock. The place seems to have partially reopened to become the temporary headquarters of the Metropolitan Police's operation in the area.

A little group of uniformed officers is gathered outside the door, radios beeping. Inside, the chairs are up on most of the tables, and most of the lights have been switched off. But one table by the window is occupied by Sherlock and John. They sit in stony silence with steaming paper cups in front of them, still in their coats, studiously avoiding each other's eyes.

SHERLOCK (after a moment, in a deliberately casual tone): You do know that even the Americans banned waterboarding back in 2009, don't you? On the grounds that all it ever induces a subject to tell their interrogators is what they want to hear, rather than what really happened?

JOHN (defensively): Well, sometimes those two things do coincide.

But to his credit, he's not looking exactly proud of himself. Sherlock gives a snort.

JOHN (annoyed): I know, it wasn't the most elegant solution. Not my fault, though.

SHERLOCK (frowning): What do you mean?

JOHN: You could just have talked to me, Sherlock. Right from the start.

SHERLOCK (evasively): You were busy working.

JOHN: No, I bloody wasn't. Not twenty-four seven, and you know it. Did you seriously believe I'd be happier never knowing what happened to her?

No answer.

JOHN: And for the record - next time you can't deduce something, just bloody ask.

He takes a sip of his tea - too hastily. It burns his tongue. John pulls a face.

SHERLOCK (raising an eyebrow): So you can walk out in a huff?

JOHN: You're not the only one who's got things in his past that he doesn't enjoy remembering, you know!

SHERLOCK (rather coolly): I told you there was no such thing as privacy in a murder investigation.

JOHN: And when was the last time you were a suspect in one of those? That doesn't exactly feel fantastic, you know.

SHERLOCK (dismissively): It certainly doesn't seem to facilitate rational thinking.

JOHN (furiously): That's not about rational thinking, Sherlock, that's about respect! Just in case you've ever heard of that concept before!

A corner of Sherlock's mouth twitches, but he doesn't reply.

Outside, a welcome distraction moves past the window: Two uniformed police officers leading the way, then a team of paramedics, wheeling a stretcher with a warmly covered figure on it, and Greg Lestrade and Molly Hooper bringing up the rear. The officials continue to the main road with their charge, but Molly Hooper turns aside into the coffee shop, the bell on its door jingling as she pushes it open. She gives Sherlock and John a quick nod, then addresses herself to the man behind the counter, probably asking for a hot drink of her own. John follows Sherlock's eyes, which have been fixed on Molly from the moment she's entered.

JOHN (in an undertone): I hope you're impressed with her, at least.

SHERLOCK: Not if she knew what you were going to do.

JOHN (quickly): Oh, no. Not at all. I only asked her to borrow a photo for the profile. But she said she wanted to help with the rest, too. Could barely dissuade her from coming along tonight to make it look genuine.

Now Sherlock does look decidedly impressed. John, seeing it, picks up his cup again.

JOHN (with a wry little smile): Well, she knows what it's like.

SHERLOCK (drily): What, to be drowned in a bath?

JOHN (pointedly): To date a dangerous criminal without knowing it.

SHERLOCK: Ah. I forgot.

But in spite of his non-committal tone, there is definitely true respect, and maybe even a touch of admiration, in the way he's looking at the petite pathologist now.

Molly, who has successfully negotiated with the management not only for tea but also for today's leftovers, now joins the two friends at their table, carefully carrying her drink and a plate with a little heap of baked goods on it. She sets it down in the middle of the table, and picks a blueberry muffin.

MOLLY (a little awkwardly): Sorry. Crime solving is hungry work, don't you find? And I did miss a dinner date. (She takes a large bite of her muffin, and sighs.) But I'm so glad we've got him.

JOHN (to Molly): Well, you got him. You were brilliant on the phone with him. He didn't suspect anything at all.

MOLLY (modestly): Oh, I just did what you told me – threw myself right at the first man who seemed more interested in the whales than in me . (With a slightly reproachful look at John) I thought we were doing it just to catch him, though.

SHERLOCK: Well, it wasn't a bad idea, making that profile to trap him. (Almost grudgingly) I might have thought of that myself.

JOHN (drily): Oh, high praise.

The door of the café is pushed open again, and Greg Lestrade comes walking up to their table. He slumps down next to Molly, and without so much as a by-your-leave picks out a chocolate croissant from her supply.

LESTRADE: Would you believe it - George Joseph Smith is actually real! (He takes a bite, then digs out his little black notebook.) He's an old friend, too. Database entry as long as my arm. (Consulting his notebook) Born in Bethnal Green, London, in 1978. Sent to a Young Offender's institution at the age of fifteen for theft and receiving stolen goods on so many counts that even his parents gave up on him. On his release moved down to the coast. Seemed to do well for a while. Set up his own business in the IT sector, and in the summer even worked as a volunteer -

SHERLOCK (smiling sourly): - lifeguard?

LESTRADE: How do you -

SHERLOCK (with a shrug): Expert on drowning. I told you so.

LESTRADE (his eyes back on the notebook): He had no head for business, at any rate. By the time he had to file bankruptcy, there were already dozens of creditors and business partners pressing charges of fraud, forgery and embezzlement against him. So back to prison for another four years or so. Got back out only in early 2009. It's definitely our man. He gave us his real name straight away when we asked him to identify himself, just now. Almost like he was glad it was all over.

SHERLOCK (drily): Well, he must have been.

MOLLY (to John, quickly): But he was responsive and all. No reason to suspect lasting damage. They're just taking him to hospital for overnight monitoring.

JOHN (quietly): Thanks.

A rather awkward silence falls. Then Molly makes a valiant effort to change the subject.

MOLLY (to Lestrade): But if he used his real name with Beatrice Mundy, he might have been serious about her at first, right? If she was such a rich woman, getting together with her for real would have taken care of all his financial trouble.

LESTRADE (doubtfully): Possible. Or else he was just being careless.

SHERLOCK: Though not as careless as he was when he killed for the third time.

LESTRADE: Why? (With a lopsided grin at John) Because he shouldn't have picked John Watson's ex?

John grimaces.

SHERLOCK (to Lestrade): Because he picked a victim who was a local semi-celebrity whose sudden tragic death made the national news, of course, leading us to the other two. (Rather snidely) If I may remind you, the fact that she was John Watson's ex very nearly enabled the killer to get away with it, while you were so very busy looking in the wrong place!

MOLLY (to Lestrade, confused): What? What are you talking about?

There is another silence, even more awkward than the first. Molly looks from Sherlock to John for answers, but neither of them seems to be willing to elaborate. Then Lestrade straightens up in his seat and clears his throat.

LESTRADE (to John, earnestly): Well, yes, that was - that was wrong. We were wrong. (A little sheepishly) Sorry, John. Actually, looking back, I'm not sure how we could ever think -

SHERLOCK (cutting him off, sarcastically): Well, it wasn't entirely unlikely. As you saw, John won't hesitate to give anyone a ducking if he thinks there's a good enough reason.

JOHN (unsmiling): Sherlock, that's not funny.

LESTRADE (to John, seriously): It's true though. We'd probably better delete what's on your phone, if you don't want Smith to press charges against you . And then we've just got to hope that what evidence we'll find in the pond on Peckham Rye Common, on Alice Burnham's old laptop and in the Mundys' empty house in Herne Bay will suffice to convict him.

Molly, who seems to have taken until now to put two and two together, turns to Lestrade in complete astonishment.

MOLLY: You didn't seriously think that it was John who - ?

Lestrade shrugs a little helplessly.

SHERLOCK (to Molly): Have some pity on our narrow-minded police, Molly. The statistics were dead against him.

JOHN (rolling his eyes in annoyance): So that's what I am, then, a statistical anomaly?

SHERLOCK (earnestly): Absolutely, yes.

The two friends look at each other for a moment. John seems rather surprised to find no more hint of irony in Sherlock's expression. Then it starts to sink in that what he's just heard amounts to no less than a rare and beautiful compliment. The corners of his mouth are just beginning to go up in a half-exasperated, half-affectionate laugh, when the bell on the door jingles again. A uniformed policeman pokes his head in.

POLICEMAN (calling across to Lestrade): Sir? The crew from the second ambulance would like to know if they're still needed.

LESTRADE (clapping his hand to his forehead): Oh, drat. Clean forgotten them.

SHERLOCK (with a frown): What second ambulance?

Lestrade pockets his notebook and rises from his chair.

LESTRADE: Same reason why we called the one for Smith, of course.

John exchanges a look with Lestrade, and immediately catches on.

JOHN (to Sherlock, innocently): Like Molly said. Overnight monitoring for secondary complications. Standard medical practice for all cases of near-drowning, you know, even for those not requiring resuscitation. (He gets up from his seat, and nudges Sherlock off his own, too.) Come on, then.

SHERLOCK (stubbornly): I'm fine, I don't -

John, not listening, starts herding Sherlock towards the door.

JOHN: Come on, or don't you want to be fit for when you replicate that little stunt for the jury in court? You're not missing anything here. The Met's got a murder suspect to process, Molly will want to get started on a new paper for the Journal of Forensic Pathology -

SHERLOCK (digging in his heels): And what about you?

JOHN: I'll take all night to type up the Adventure of the Brides in the Bath for the blog, of course. (He holds up his index fingers and waggles them in front of his friend's face.) Five words a minute, remember?

Sherlock scoffs. John invitingly holds to door open. Sherlock lets himself be escorted outside, though still radiating disapproval.

MOLLY (to Lestrade, in a worried undertone): Sherlock near-drowning, too? What's all that about?

LESTRADE: Your paper. (With a resigned sigh) I'm sure he'll be proud to give you all the details tomorrow.

They follow Sherlock and John out of the café, and fall into step side by side.

MOLLY (nodding at the two friends walking ahead): Will they be okay though, d'you think? That's quite a lot of broken china.

The voices of Sherlock and John come floating back towards them, still bickering.

JOHN: I'll ask your brother to sit with you if you like.

SHERLOCK: Don't you dare, John Watson!

LESTRADE (to Molly, with a smile): Mending already, wouldn't you say?

Molly smiles back.

THE END

December 2016

Endnotes:

I'm hugely indebted to RubraSaetaFictor who - in the temporary absence of my regular beta-reader Cooklet - very generously agreed to beta-read this story, and did so both with the eyes of a hawk and at the speed of lightning. Thank you SO much, dear - without you, this story would never have seen the light of day before season 4, and probably never at all.

I'd also like to thank
- Wellingtongoose for her excellent medical "Sherlock" metas, which have been extremely helpful in shaping my headcanon about John's present and past medical work;
- Cooklet for some preliminary discussion on what exactly convinced Sherlock in the first place that Molly Hooper of all people would make a suitably discreet and cool-headed conspirator for the Reichenbach deception; and
- maryagrawatson for medical advice on first aid for near-drowning, and for cheering me on during the writing process.

Thank you also to all who "favourited" and commented, and may still do so - your feedback, big or small, is always very much appreciated! :)

Now, enjoy season 4, everyone! Unfortunately I won't be able to see the new episodes the moment they air in the UK, and I'll be trying to avoid big spoilers. So if you feel an urge to talk to me about them, please check my profile first whether I've seen the episodes yet or not. :)

To conclude, for those of you who are interested, some editorial notes on the original case of the Brides in the Bath, and a little glimpse behind the scenes of its fictionalisation.

As some of you may have realised or guessed while reading, this story is based on a real, historic case. The case of the Brides in the Bath, as it quickly became known, was investigated and solved by the Metropolitan Police at the time of the First World War. It inspired both the main storyline and many details in the story you've just read.

Just like the character in my story, the real George Joseph Smith ruthlessly preyed on unmarried young women, promising them a safe, happy life with him as a loving husband. In fact, he ripped them off in the most unscrupulous manner, including killing three of them for their inheritance and/or insurance money as soon as they'd signed the relevant papers.

Under a different alias each time (including "Henry Williams", "John Lloyd" and "Oliver George Love"), Smith entered into no less than seven bigamous marriages. In most cases, he merely made off again after a few weeks with his "wife's" belongings and money. In three cases, however – those of Beatrice "Bessie" Mundy in Herne Bay (1912), Alice Burnham in Blackpool (1913) and Margaret Lofty in London (1914) – Smith "found" the women drowned in their bathtubs, with their heads under water and their feet up. They had all made wills in Smith's favour, and/or taken out a life insurance with Smith as the sole benefactor, shortly before. In all cases, the coroners' verdicts ruled death by accident or misadventure, assuming that the women had died from sudden heart attacks, or drowned in fits of epilepsy or similar seizures. No traces of violence had been found on any of their bodies.

Twice, Smith cashed in on the deaths and moved on, unchallenged by the law. Back at a time when there were no ID documents, and press coverage of strange incidents and accidents was mostly restricted to the local level, nobody made a connection between these deaths.

But when Smith killed for the third time, he made – as our BBC Sherlock would put it - the one mistake that serial killers must always make to get caught. He killed Margaret Lofty in London rather than in a more provincial place. That meant Lofty's death was reported in a London-based nationwide newspaper, the News of the World. It thus attracted the attention of Smith's and Alice Burnham's former landlord in Blackpool, a Mr Joseph Crossley. He contacted Scotland Yard, pointing out the striking similarities between Margaret Lofty's and Alice Burnham's deaths. This was also reported in the papers, which in turn alerted the local chief police officer at Herne Bay. The good man immediately brought another similar case from his own jurisdiction - that of Bessie Mundy - to Scotland Yard's attention.

After an intense investigation, including many witness interviews and the exhumation of all three victims for new post mortems, the Metropolitan Police concluded that the same man had been involved in all three cases as the victims' supposed husband, and George Joseph Smith was arrested. This was achieved with the assistance of Margaret Lofty's life insurance company, who lured Smith to their offices by pretending to be willing to satisfy his claim.

Even after Smith's arrest, it remained a mystery how exactly he had managed to kill his "wives" without leaving traces. Smith himself wouldn't tell. Scotland Yard therefore consulted Dr Bernard Spilsbury, one of the first Home Office pathologists - a new post recently created to acknowledge the growing importance of medical expertise in criminal investigations.

Dr Spilsbury, although he was considered the forensic capacity in the United Kingdom at the time, found no proof of either natural death or of violence or poisoning in any of the three victims' bodies. He thus decided to set up a rather unorthodox experiment.

Together with Detective-Inspector Neil, who was in charge of the investigation at the Met, Spilsbury hired several experienced female divers of the same size and build as the victims to reconstruct the crimes in the original bathtubs in which they had happened. It turned out that quickly pulling up the feet of the test persons, so that their heads slid under water in a rush, resulted in immediate loss of consciousness while leaving no signs of foul play. It reportedly took half an hour to revive one of the poor guinea pigs, but it proved the killer's MO to the satisfaction of the investigators.

It convinced the jury, too. George Joseph Smith was charged with murder, tried at the Old Bailey, found guilty, and sentenced to death. After his appeal was rejected, he was hanged at Maidstone Prison in August 1915.

The exact medical explanation for Smith's killing method remains unclear. The explanation I have offered in my story is the most specific and the most plausible I could find. Strangely enough, there seem to have been no copycat cases that might have led to more recent forensic research into this question. A man was convicted of killing his lover in the same way in South Australia in 1995, but the conviction was ultimately overturned - though more due to a general lack of evidence than due to a detailed medical analysis of the scenario.

If you'd like to read up on the original Brides in the Bath case, try the Wikipedia article on George Joseph Smith, or the George Joseph Smith profile on Murderpedia. The "History by the Yard" website has a good summary, too, as has the official website of the Metropolitan Police, in their "Historic Cases" section.

But why a fictional rewrite? And more specifically, why a Sherlockisation?

Because I feel that the original story of the Brides in the Bath has lost nothing of its topicality even a century later.

It still comes pretty close to home. I readily admit that it freaked me out when I first read about it. Those crimes represent such a gigantic betrayal of trust, and that's unfortunately a timeless danger.

In the 21st century western world, social pressure on women to find a husband at all cost has of course abated significantly. All single women who are looking for a partner remain at risk, however, of finding themselves the victims of men who look for something much more mundane than love.

Actually marrying someone who is not who they pretend to be has become almost technically impossible these days, too. But in the world of online dating, it's still as easy as it was in 1914 to put on a different persona and tell fairy tales about oneself to impress a potential partner. And sometimes the damage - emotional, financial or even physical - is already done by the time the wolves drop their masks.

Law enforcement officers will look twice these days if the victim of an unexpected death has only just made a will or taken out a life insurance in favour of their partner. So today, con artists usually have to come up with more creative ways of relieving their unsuspecting partners of their money. But they still do.

And it remains a worrying fact that - be it due to lack of training or lack of awareness on the part of medical and legal professionals - even today many deaths that should raise eyebrows still get assigned much too quickly to natural causes or accidents.

But Smith's case also presents – as Sir Arthur Conan Doyle's Holmes would have put it – several other features of interest.

Smith's trial is one of the earliest examples in British legal history in which a conviction was secured almost exclusively through forensic evidence - at a time when the concept of forensic science as such was still in its infancy. Smith himself protested his innocence literally to his last breath. So the jury had little to go on - apart from the extreme improbability of one and the same man losing three spouses in three years through the same rare kind of accident, which was technically still no proof of his guilt. By the standards of 1915, the jury took a real leap of faith when they went with little more than Dr Spilsbury's evidence of how the drowning must have been accomplished to pronounce Smith guilty.

The investigation also marks one of the earliest uses of what is today called forensic profiling - the comparison of individual characteristics, circumstances and peculiarities of several separate crimes to establish patterns that lead to the identification of the perpetrator.

But quite apart from the moral and legal lessons to be learned from it, the case is just a fantastic story. It was absolutely begging for a fictional retelling, and - to me, at any rate - it was specifically just waiting to be transferred into the BBC "Sherlock" universe.

Our BBC Sherlock would have loved it. The puzzling lack of medical evidence for the causes of death; the almost fantastical coincidence that lead the investigators from the last death to the previous ones; the general attraction of dealing with a ruthless serial killer… Dogged police legwork combining with almost frightening audacity in the name of science to hunt down a murderer whose greed, in the end, is his downfall. Sherlock would say that's Christmas three times over.

And isn't Dr Spilsbury's reconstruction of the crime - which is of course highly unethical by modern standards - exactly what Sherlock would do to prove his point, even with himself as the guinea pig?

All the original cast of characters also translated just perfectly both into "Sherlock" canon characters and into modern OCs.

On the one hand, a chillingly unscrupulous serial killer, and his innocent and truly pitiable victims, driven into his arms just as much by societal pressure as by his own carefully constructed fairy tales.

On the other hand, a wonderfully congenial duo of investigators that is so very familiar to "Sherlock" fans - the experienced, highly competent and hard-working official detective from the Met, and his glamorous, unorthodox forensic consultant.

Unfortunately at first, with the roles of DI Neil and Dr Spilsbury already taken by Greg Lestrade and Sherlock himself, there seemed to be little room for John in the Sherlockised version. But sometimes solutions present themselves suddenly and unexpectedly. I intended no disrespect to the memory of Margaret Lofty when I changed her name and identity to that of Jeanette from "A Scandal in Belgravia", but when I realised what might happen if I gave the last victim the name and face of John's ex-girlfriend, I just couldn't resist. Just to clarify: No honourable ex-army doctor was ever suspected of the killings in the original case.