It's been three months since that strange night in Baker Street. Life for me has changed – I have a new job and am working full time in the chemistry department at UCL. It's a nice crowd, the department head is a lovely and very supportive lady, and I am enjoying myself. There are some nice men in the group, too, but I am finding that nobody is making much of an impression on me these days. There has been no word from Sherlock Holmes, and I have come to the conclusion that I will not hear from him again. That does not, unfortunately, mean that I have been able to move on. I believe I am beginning to get a reputation for being a hard catch, but it does mean I get left alone and that suits me.

Just after lunch this Tuesday I am making my way back from the canteen when my telephone beeps with a text alert. I check my phone.

"221B Baker Street. Now would be good. Take some leave. SH," it says.

I stop dead. The girl behind me bumps into me and I mumble an apology, moving out of the flow of traffic. My hands are shaking, and it takes me a moment to regain my composure. I'm not sure what to do. The sensible part of me is telling me to ignore the text, stick with the easy life, keep walking and just get back to work. What is he thinking contacting me like that after all this time, anyway? I remember what happened last time, how I was sore for days after, and John's warning.

"He's not safe, Sherlock. You need to be careful."

But all sensible thought is being drowned out by a compelling urge to just walk out the door and head straight to Baker Street, whatever may come. It isn't quite that simple though, and I need to sort a few things out before I disappear. Thankfully things are quiet at work and once I have made my mind up that I am going – obviously common sense is irrelevant when it comes to my reactions to Sherlock – it is easy enough to take the rest of the week off.

My manager, Sophie, is a little surprised at the immediacy of the request, but I manage to invent a fairly convincing excuse of family issues which she seems happy to accept. I make my way out of the college and decide to walk to Baker Street, hoping that I will be able to make myself look calm and composed in the meantime.

I stop in front of the familiar door, and knock. This time I have few second thoughts, although I am feeling apprehensive about what I am here for. Three months ago, in a moment of madness, I offered him the use of my body for scientific purposes. I am sure he has not forgotten. The door is opened by Mrs Hudson, who looks pleased to see me.

"Oh hello dear", she says, "come in, I'll bring you right upstairs. I do think they're waiting for you".

So, I'm expected then. I hang up my coat in the hallway. She leads me up the stairs and knocks on the door. "Hoo-hoo. She's here!" she says around the door before letting me in.

The room is exactly as I remember it: cluttered with paperwork and fascinating objects. Skull on the mantelpiece, gnu with headphones, books everywhere. John Watson is sitting at the desk with his laptop, looking, for want of a better word, homely. Sherlock is standing looking at the wall, which is covered in pieces of paper. I try not to stare at him, to let it show how much I have missed seeing his imposing figure. He is looking as impeccably dressed as I remember, focussed, restless. He doesn't acknowledge my presence, palms of his hands pressed at his chin, bottom lip resting on his fingertips. I find it hard to keep my eyes off him, but I also feel very nervous. John says hello.

"I hear you've got a new job?"

I am grateful he has broken the silence, as I am not sure what I am doing here. "Yes, I went back to UCL. It's good. I was only around the corner just now."

He nods. "sounds great. Tea?"

I say yes, that would be nice. He goes off to the kitchen, leaving me still standing aimlessly in the room. I look over at the wall that Sherlock is studying. It is covered in a map of London surrounded by photographs, which are connected to the map with bits of string. Sticky notes are spread around the map and photos. It's an elaborate thing, and it looks some time in the making. I move a little closer to see what the notes are saying. There are dates and times, names, numbers. All of the photographs are of women, by the look of them in their early twenties.

"Look at this, John." Sherlock says, pointing to something on the map. He looks over at me, then stops. He looks a little disturbed.

"Adriane. Where's John?" I realise he really hasn't heard me come in.

"He's in the kitchen, making tea," I say.

Sherlock looks me over, then turns back to the map. "Still single then," he says, "and not even looking."

I open my mouth to respond, but no words form. I wonder how he figured that out. I also hope he won't extrapolate the thought and work out why I am not looking.

"It's written all over your clothes, your hair, the way you carry yourself. Good to see the new job is working out though."

I'd forgotten about the mind reading.

"Lucy Smith, twenty-one, disappeared late evening near Guy Street Park two weeks ago after a minor row with her boyfriend," Sherlock says, pointing at one of the photographs. It takes me a minute to work out that he is explaining his current case to me. He points at another photograph.

"Sarah Overton, nineteen, disappeared near Tanner Street twelve days ago, while walking home alone after a night out with friends."

The photograph shows a smiling young woman. She's pretty. Another photo.

"Suzanne Wright, twenty-three, disappeared last week near Tabard Gardens while visiting a late-night shop to get some supplies for her partner and young child."

A knot is forming in my stomach. I wonder where this is going. He points to the next one, relentless.

"Emily Taylor, twenty, disappeared from outside her flat on Law Street seven days ago. She lives alone, we don't know why she went out or the exact time she disappeared."

A girl on her own, just like me, in just another normal street in London. Sherlock points to the last photograph, showing a beautiful blonde girl holding a laughing baby.

"Alison Brown, twenty-four, disappeared yesterday night while walking back home from the Soho Gyms, leaving her husband and a six-month old daughter."

I'm feeling a little sick. The pattern is obvious even to me. I remember seeing something about Emily in the paper but I haven't heard about the other ones.

"The police are trying to keep it out of the news," he says, looking at me, "it won't take long for this to get into the papers though. We don't have much time."

I am giving him a blank stare. I have no idea what he expects me to do. He walks over to me – too close – and says, "I need your help, Adriane."

-oooOooo-

"Tea," says John, coming back into the room.

Sherlock takes a step back, giving John an odd look, and takes his mug. John gives me mine, and then goes back into the kitchen for his own tea. Sherlock gestures to the sofa, "Sit down."

I sit down, but he remains standing. There is something odd in his manner, he seems tense and impatient, but it is as if he is trying to contain it, to not let it show. I guess it must be to do with this case. John comes back in with his own tea and sits back down at the desk.

"Five women," Sherlock says, "Disappearing in the space of two weeks. All were on their own when they vanished, and they all went missing at night. They were all young, none of them suffered from any type of depression or serious problems at home, and all could be considered pretty."

He looks across to John for confirmation, who nods his agreement. I look again at the photographs from where I'm sitting. They all look gorgeous to me, and I just don't understand how Sherlock can be so cold about this. I can't help thinking about the two girls with children. The families must be frantic. And yet there he stands, sketching out this case as if it is an interesting puzzle. He walks back to the map, grabs a marker and draws a circle around the locations where the disappearances have occurred.

"They have all disappeared from a relatively small area in London, but so far the police have drawn a blank. There have been no bodies or ransom demands, suggesting they were taken for a different reason. Human trafficking comes to mind. By now, they could be anywhere."

He looks momentarily angry. "If only they'd seen fit to bring me in on this case from the start, we wouldn't be in this situation." Then, quietly, he says almost to himself, "There's nothing for it. There really is no other way."

John cuts through. "But they are searching the whole area at the moment, Sherlock. They have trebled the police presence in the last few days. Customs and the coast guard will be on the alert. Surely they'll come up with something."

Sherlock looks scathing. "Pha. The police invariably miss the obvious. With a bit of good organisation and a small boat they can easily circumvent Customs and the coast guard. I wouldn't hold out any hope in that direction."

He looks at me again, intense, serious.

"As far as I can see there is only one way we will be able to locate them quickly. But it would be perilous, especially to you, Adriane. And you would be on your own."

Perilous. That's a very beautiful word, I think, for a very bad concept. I am beginning to see what he is expecting from me. John has come to a similar conclusion.

"Sherlock, no, you can't be serious?"

Sherlock is ready for the challenge, and puts the force of his frustration behind his response. "Just think about it, John. We are dealing with a professional gang here, that much is obvious. These girls will be out of the country in a matter of days and will never be heard from again. They will be trafficked to God knows where. Unless we act quickly and actually find them, get to them, we may as well give them up for dead now."

John looks absolutely horrified. "You are seriously suggesting… what? Putting Adri out there for bait? You're mad!"

Sherlock's stance has gone calm, icy. "Unless you have a better idea, Doctor. Or we could just wait here for the police and coast guard to finish their excellent searches."

John just stares at him in disbelief. Sherlock looks at me but doesn't ask the question. I am frozen on the spot, not knowing what to think or say. He relaxes a little, and says, "Look, it would be easy. We know where they are operating. We know the kind of people they are targeting. And the right kind of technology and a bit of skill could lead us straight to them."

I am waiting for him to explain exactly how this would work, but he seems to think he's said enough. He sits down at the other end of the sofa and looks straight at me. "This is no longer a matter of science, Adriane," he says calmly, "I wouldn't need to ask if it was. It is a matter of life and death."

Quite apart from the reminder that I should expect to be available for scientific experiment without question, there is no doubt that what he is asking of me is a mad, dangerous, indeed perilous thing. It could end badly in any number of unimaginable ways. I am wondering why I came back here. Unfortunately, the answer is sitting right next to me on the sofa, observing my internal struggle.

To get away from his unnerving stare and to get my thoughts moving, I get up and walk across to the wall. I look at the photographs. Happy, smiling faces. Normal girls going about their everyday lives in London, ripped away from their families, to be… used, trafficked, sold, into a degrading existence, probably a short one at that. They didn't get asked, I think.

I remember a darkened classroom at Roland Kerr College, the first time I saw Sherlock, utterly defiant in the face of death, amused at the very thought of it. He does this every day. It's the face of the baby that tips the balance in the end. Although the thought crosses my mind that I have been skilfully set up, it doesn't matter anymore. I look at John, then at Sherlock. John is looking drawn, worried, obviously hoping that I will say no. Sherlock is just watching me, his face expressionless, and only the slight narrowing of his eyes gives away the fact that he is impatient for an answer.

"OK," I say, my voice not sounding quite as calm as I had hoped, "I'll do it."

John's reaction is not what I expected. I thought he would jump up, shout maybe, but he just slumps back in his chair, covers his face with one hand and sighs.

"God, no…"

Sherlock gives me a brief look of triumph, mixed with something else – pride? He is so hard to read. "Good," he says, getting up, "there's a few things we need to do." He's all action now, a spring released, charging ahead.

"I had a look, but to be honest your wardrobe is atrocious. I got you this, though." He throws me my handbag, the one that I use for nights out. From my flat.

"There's some shoes as well," he says, pointing to what I recognise are my best shoes sitting in a corner. I look in the handbag. Make-up, lipstick, hair brush, toothbrush, toothpaste. Everything a girl needs for a night out. I look at him.

"You went to my flat," I say. I can't quite keep the astonishment from my voice. He just gives me a deadpan stare and says, "Clearly."

From the corner, John says, "Sherlock…"

"Look," Sherlock says, looking irritated by this trivia, stopped in mid-flow, "I saved us a lot of time. I got everything you need. Is there a problem?

There is a clear, impatient challenge in his last words. He's standing in the middle of the room, knowing full well he is looking intimidating, waiting for me to back down. I can't help myself.

"It would be nice if you'd asked," I say.

He just raises his eyebrows and turns away, superior smile in place, happy in the knowledge that he has won. What if I'd said no? I think. What if I had refused to help? But I was always going to agree, and he knows that, and so he's done the logical thing and got stuff ready. Even when that meant breaking into my flat and rifling through my belongings. I look at John, who rolls his eyes at me. I guess this isn't the first time something like this has happened. I can't help but notice that he's looking very worried.

"John, I need you to go into town and buy Miss Woodford something decent to wear. Something I'd be seen with," Sherlock says.

John looks at him, shaken from his worries.

"What?"

"She needs some clothes, John, something better than that," he waves his hand vaguely in my direction. I check my outfit. I didn't think it was that bad.

"You've got a reasonable eye for women's dress. Size twelve, don't forget the tights."

John stares at him, then back at me. I shrug, trying not to let it get at me. There doesn't seem much point in arguing, and he got the size right.

"Why, where are you going?" asks John, obviously wondering why he is being sent on this errand.

"We're off to Bart's," Sherlock says, grabbing his coat. "Back here in an hour, John. Come on, Adriane."

I give John a final confused look, which he returns, and run after Sherlock. He is already out of the front door, hailing a cab. When one pulls up he holds open the door for me and I get in. The taxi ride is a quiet one. Sherlock is deep in thought, and I honestly don't know what to say. I feel like I am once again falling down the rabbit hole, but while the last time the rabbit whole was comparatively safe, this one has got monsters in it. I am also conscious that I didn't so much fall as was skilfully tipped into it. I am trying to imagine what might happen to me, then realise that it is better not to think about it as a host of graphic images flash in front of my mind's eye. I can't suppress a shudder, and Sherlock picks up on it. He looks at me.

"Scared?" he asks.

I nod, "Yes." There is no point in denying it.

"Hm," he says, then looks out of the window again. Just another factor in a big equation, I guess, filed for reference. It doesn't help me very much.

Eventually the taxi pulls up in front of St. Bartholomew's Hospital. We get out, and Sherlock leads the way until we get to a small lab. He hangs up his coat and starts pulling things out of drawers and cupboards. I notice syringes and swallow hard. Not my thing, at all, ever. Then he goes over to the fridge and takes out a number of glass ampoules. When he has a tray full of stuff, he gestures to a chair.

"Take off your coat and roll your sleeve up," he says.

I hang up my jacket and sit down, no doubt looking apprehensive.

"Ehm," I say, "can I ask what all this is?"

He looks at me, distractedly, as if I have just asked a completely irrelevant question.

"What? Oh." he says, obviously realising that an explanation might be in order. He points at the glass bottles. "Insurance. Vaccinations. We don't know what they'll do to you. Hep-A, Hep-B, HPV, and a general antibiotic. That one took a bit of getting," he sounds pleased with himself as he points to an unlabeled bottle,
"But I think you'll want it. It's an experimental HIV vaccine currently on trial with the FBA."

I haven't quite taken all this in and it takes a moment for the implications to hit me. He is going on the assumption that they will rape me, I think. Also, it seems that he has planned this some time in advance. I wonder how long.

He looks at me, and says, "problem?"

"No," I say, "Yes. How long have you been planning this?"

He looks guarded when he replies, "Only since yesterday evening. I wasn't sure this was necessary before then."

I shake my head, there's nothing I can say to that. I am still holding my arm defensively close to my body. He is getting a syringe ready, skilfully removing the air in the needle, and gets an antiseptic wipe. He holds out his hand, obviously expecting me to offer him my arm. He raises an eyebrow when I don't comply.

"OK. I don't like syringes. I hope you know what you are doing," I say.

He gives me a stony look, and says "trust me, I do."

There is something unspoken there, but there is a warning in his eyes telling me not to pry. I give him my arm, looking the other way.

Sherlock has just administered the final injection when the door of the lab opens and Molly Hooper enters. She stops when she sees Sherlock, and then looks at me a little suspiciously.

"Ah, Molly," says Sherlock.

She doesn't look very sure of anything when she says, "What are you doing?"

Her eyes are on the syringes. Sherlock straightens up, trying to judge the situation.

"Molly, this is Adriane Woodford. She is helping me on a case," he says.

I say a very quiet "hi." She just looks at me, and then back at Sherlock.

"Anything I could have done?" she asks.

It is clear Sherlock hasn't got time for this. I guess having to restrain himself this afternoon at the flat while getting me to agree, John's obvious disagreement and my own hesitance haven't improved his mood. He sighs, and says, "I am about to set Adriane up to be abducted by a gang of sex traffickers. Chances are she will be raped in the proceeds, and if we're really unlucky she might get herself killed before we can discover their hideout and get her back. I am giving her some vaccinations so that at least there's a chance she won't catch Hep-B, or worse, while she's out there. Would you like to swap places?"

His tone is sarcastic, and he ends his short tirade by fixing her with an evaluating stare.

Molly has gone as pale as a sheet. I am not sure I look any better, all the blood has drained from my face after having the danger I am putting myself in described so matter-of-factly. She looks at me.

"Is that true?" she asks, in a shaky voice.

All I can do is nod.

"So, I'd appreciate it if you could stop being jealous, and give me a hand," Sherlock continues, oblivious, or indifferent, to the level of shock he has caused in both of us.

"Yeah, sure," Molly says, vaguely. "What am I doing?"

"There's a sachet with a microchip in the pocket of my coat. Get it for me," Sherlock says. He is rummaging in another drawer, "Ah."

He gets out another syringe, but the needle on this one is enormous. I've seen these, I had my cat microchipped some years ago and it nearly made me faint then. I feel dizzy. Sherlock grabs another chair and sits down. Molly passes him the microchip. He looks briefly at me, inserts the microchip into the syringe, then looks at me again, more searchingly this time. I have no idea what I look like, but it makes him stop.

"Molly, get Adriane a cup of tea and a couple of biscuits. We're going to have to wait a moment."

He's looking amused now. I don't think it's very funny. Molly leaves the room, and I try to find my composure.

"Sorry," I say, not looking at him.

He's still looking at me, making me feel very uncomfortable. I'm wondering if he thinks I'm not up for this. I look up, but he doesn't seem all that concerned. Instead of the scathing remark that I was expecting, he holds up the syringe again.

"This," he says, "is a GPS transponder chip. It is not in production yet. Not a lot of them have been tested. I am putting it here," he touches the skin behind my collar bone, "Because I hope nobody will notice it there. And with this," he picks up something that looks like a small remote control from the lab table, "I will be able to locate you anywhere in the world. OK?"

It helps. I nod, and say yes. A few minutes later, Molly comes back into the room carrying a tray of tea and biscuits.

"I made everyone one," she says.

"Thank you, Molly," says Sherlock.

He passes me my tea and puts the biscuits in front of me. They are both watching me now, and I just feel silly. I give a nervous giggle. "Stop staring at me."

Molly moves away, but it doesn't stop Sherlock. After I have had a biscuit and a few sips, he picks up the syringe again. "Ready?" he asks.

I nod, sit back and close my eyes. Although it hurts, it's not as bad as I expected, and he is very quick.

"Done," he says, wheeling his chair back and picking up his mug, "I take it you don't need any contraception."

I just shake my head, beyond shock now, and finish my tea. Molly comes over and pinches a biscuit. It is a strangely peaceful moment in what has been an afternoon filled with madness so far. It doesn't last long. As soon as Sherlock has finished his tea he jumps up and gets on his coat.

"Time to go," he says, throwing me my jacket.

Molly gives me an anxious look, and quietly says, "Good luck."

I don't know what to say back, so I just say, "Thank you for the tea."

Sherlock has already gone out of the door, not even bothering to say goodbye to Molly. I run after him.