John's phone beeps. He looks at it. Sherlock is driving again, of course.

Congratulations. MH

John's cheek twitches. He has spent considerable time and effort avoiding Mycroft. He'd hoped that his obvious lack of interest in anything the man had to say might put him off. Clearly not.

He does not know what to reply. Perhaps: No congratulations are required? There is nothing to congratulate me about? Piss right off and leave me alone?

It all seems wrong and yet the message sits there on the screen, burning him. Mycroft's assumptions and interferences hurt.

Sherlock is back. John is glad. More glad than he has ever known. But although things are calmer today, things are not instantly back the way they were before. A friendship without secrets could not be mended so quickly. A friendship like theirs - may never be the same again.

Do you think your brother has simply made me happy?

He clenches the phone in his fist and puts it back in his jeans.

"Mycroft," says Sherlock, eyes on the road. They are approaching the river and will soon be in east London.

John looks at him.

"No one else makes me want to stamp on a phone," Sherlock says. He slides his eyes sideways at John. "I have certainly not missed his constant meddling."

John doesn't respond to the Mycroft thing, but asks, "Where are we going?"

"We need to find Crash and get the police involved. Straightforward. Could have done it last night but felt too tired."

Sherlock is missing out part of the plan. John knows this. Sherlock does it instinctively: leaves John out of the plan. There is usually a reason for this, but still. It rasps against raw places.

"It's a place called Midnight," says Sherlock. "I have no idea where or what that is but we need to identify it and collect Crash. Both Crashes."

"Midnight," says John in surprise. "That's a nightclub opposite where I work."

"I can't wait to get out of these clothes," Sherlock says as they drive through the Rotherhithe Tunnel, under the Thames. The ceiling lights pass overhead in an even sequence, mesmerising. "I feel... unauthentic." He wriggles irritably.

John is not about to comment on Sherlock's outfit. It does look very strange though, and more so under these strobing tunnel lights: pale blue polo shirt, blue jeans, some kind of walking boots. Sherlock habitually dresses to intimidate, and this getup is the opposite of threatening. The short hair, too: weirdly it makes him look more vulnerable and gentle than the flowing curls did. And something about the hands. In these clothes, they seem more connected to the rest of his body, not merely emerging from the tailored suit sleeves as bodiless wrists. His wrists have always been sensual, of course. But now they are sensual and with a body attached.

Such thoughts. These would be the thoughts that John has only last night promised himself he would put away. He sighs at his own hopelessness. He doesn't really mind. It has always been hopeless, right from the start. Everything about them has. It's fine.

"What?" Sherlock asks sharply as John sighs.

"Your clothes are all still in the flat," John says.

"I can't go back there. Mycroft will be looking for me. And you." Making lane changes, watching the traffic, brimming with energy now.

"I know how to hide," says John.

"He always found you before. With the cameras."

"I wasn't trying not to be found. Come on, I can get us into Baker Street without him knowing a thing." Has Sherlock forgotten John? Forgotten what he can do? Or did he subscribe to the accepted view, that John has spent months useless, wrapped up in misery?

"Can you?" Sherlock's tone: frank surprise.

"Yeah. Done it loads of times."

Sherlock is giving him a funny look. Respect? Puzzlement.

"Yeah, 'cos you're the only person who doesn't like his private life being snooped on." John rolls his eyes. Sherlock exists at the centre of Sherlock's universe. Everyone else is background detail.

"I didn't know it bothered you," says Sherlock.

John shrugs. There are a lot of things you don't know. "You never asked."

A brief silence. Sherlock may be processing John's comment or, more likely, he has moved on and is considering their next course of action.

"Let's do this Midnight thing," John says, "and then I'll get us into the flat and you can make yourself look like Sherlock Holmes again." he pauses. "It must have been weird, all that time not being yourself." This is how Sherlock phrased it to him, explaining.

Sherlock stares ahead, the tunnel lights pulsing over his face. "I wish I'd had you with me," he says, and then they are out of the tunnel and he winds down his window to throw coins into the toll bucket.

John blinks. Sherlock seems sincere. Seems sad.

John's throat clenches. Might as well say it now as any time. "I missed you too," he says lightly.

They stare ahead, and then simultaneously turn to make eye contact. It is like a flashbulb, painful, bright, a moment to flinch from even as the photographer is saying, everyone look this way now. And then the thing is done and they refocus on the road, and the route, and the tasks they must complete.

John slept for several hours last night in the back of the van, but now he feels as if he could sleep for a week, untouched by dreams.

A nightclub in daylight: a drab, dirty place smelling of sour beer and sweat.

Midnight is trying to be classy, is going for a certain clientele, going for gothic luxe. But it is failing. John switches on the lights and sees blood red walls and gilt mirrors and more mirrors on the ceiling and ornate wrought iron spiral staircases leading up to little platforms where, presumably, the keener customers can dance for the entertainment of the others. Or maybe it is where paid dancers perform. He does not know enough about club culture to be sure. It seems trashy, not luxurious.

There is a long bar finished in copper, curving around two sides of the room. Drinking is big here. The dance floor occupies the centre of the space, with plush booths around the remaining two edges.

Upstairs is a viewing gallery, in a sloping-glass room like a sports commentators' box. More wrought iron stairs wind up to this, and across the entrance to the stairs is a thick rope. VIPs only, then.

Sherlock closes the fire door behind him and looks around, taking it in with his calculating eyes as if he routinely assesses would-be-gothic nightclubs in the course of his day to day life. "Not enough curtains for a truly Victorian gothic ambience," he comments. "But then that would retain the smell even more powerfully than the revolting velvet upholstery already does."

He whirls away, his movements the same in polo shirt and blue jeans as in his black Belstaff coat, graceful and precise. John envies him that poise and his carelessness of his own physical presence. Like an athlete, or a dancer: moves without needing to consider it, the mind in total control of the body at a deeper level than merely controlling the arms and legs.

John follows Sherlock up the VIP stairs.

The gallery is done out in a way which makes John think, manufactured madness. Curtains, if that's what Sherlock really wanted: the whole back wall is draped in heavy velvet. Dark wing chairs are grouped around little ebony coloured tables. Wall mounted candelabras, with writhing figures support artificial candles. Low velvet pouffes are arrayed to the front of the gallery so the VIPs can lean over the dance floor with their drinks and pick out partners, lovers, rivals. The carpet is patterns with large blotches and dots, dark red against grey, and John has to blink for a moment. "Blood spatter," he says then, and Sherlock sniffs.

The ceiling here is mirrored too, at a slight angle, and John keeps catching glimpses of himself and Sherlock, tops of heads, hand gestures, as they explore the area.

It has its own bar, with elaborate optics. Instead of upside-down bottles held in little clamps, there are jars like chemists' jars, with curly clear pipes leading away down behind the counter. The glasses are shot glasses but shaped like miniature chalices. The Gothic thing again, it is clearly meant to recall a laboratory.

"This isn't it," Sherlock says in irritation. "We checked the office. Nothing. No sign, no link. No sign of connection to their delivery method. No sign of the wretched pens. Nothing. This can't be the place."

John shakes his head. "Too much of a coincidence, don't you think? Crash, the Hands, and this place, all on the street where I work. There's something here. I don't know what though."

"No."Sherlock flops down in a wing chair and presses his fingertips together. "Have you got your phone?"

This again? John hands it over and drops into the chair beside Sherlock's.

Sherlock looks through. Finds the text from Mycroft and scowls, glancing at John. John shrugs. Whatever. Sherlock texts: "Sherlock, where are you? My hand hurts. I feel bad."

Presses Send.

John gives him a quizzical look.

"Mycroft," says Sherlock. "Just a hunch."

"You don't do hunches," says John.

"Ok, not a hunch. An experiment. See how closely two things are linked."

"Am I supposed to not know which number is yours and which is your brother's?"

"You are clearly in distress and thinking even less coherently than usual." He still has John's phone.

Now he shoves his hand into his own pocket and gets out his phone. Googles. How did he cope in the wild? John watches as he types another message to a number he has copied off the internet. This one reads: "Data is in place. Payment required."

He gives John his phone back. "Ok," says John, "who else have you just tried to attract to my location?"

"Echelon," says Sherlock.

"What? Who?"

He gives John the look which lets John know how stupid he is. "Echelon. The listeners. The people with the giant white balls on the tops of hills. Supposedly they run every bit of voice and text data through enormous computers, picking up key words. Bomb, terrorism, et cetera."

"But you didn't use any of those words."

"Because that's not how it works."

"So how does it work?"

Sherlock just looks at him and does not reply.

"Right. Fine." John sighs. "So what did you just do exactly?"

"The listening program does work but it is very slow. About three months to a year behind, depending on the data being monitored. This was quicker."

"What?"

"I just emailed them."

He looks at John. He is waiting. Seems uncertain, even nervous. Testing John's reaction.

John looks back. Sherlock emailed the secret government monitoring service. The people with the giant white balls. He gives in. "Ok, all right. It's funny." He sighs a smile and sees Sherlock's face lift.

It lasts a second. Then Sherlock is away, frowning, checking his phone for replies. Nothing yet. Evidently neither Mycroft nor Echelon believes in impulse moves.

Sherlock is nodding to himself. John does not question it. What would be the point? Sherlock knows what the plan is. John does not. Situation normal. Sherlock relies on him to react in the correct way. At some level that is flattering. And John would never agree to the plans if he knew them in advance. Sherlock is clever and knows this, of course, and so this is how they go on.

"John - does your hand actually hurt?"

Sherlock reaches out and takes John's hand without preamble, and examines it as you might inspect roadkill on your tyre. His lips curl in revulsion. His fingers peel back the dressing without asking permission and he bends his eye close to the wound where Priya's scrape lies alongside the one Lestrade's medic gave John before.

"Yes, it does actually hurt," John says. "Especially when you prod it, get off." He tries to move his hand away but Sherlock has a strong grip and was prepared for him to try.

"Think you could stand another scrape?" Sherlock asks, still squinting at the moist wounds. He turns John's hand over and looks at his palm, his wrist, his fingernails, back again to look at the wound, his eyes flickering.

"What? No thanks." John lets his hand go limp before Sherlock sprains his wrist.

"Might need to," Sherlock says casually, dropping John's hand.

John tapes the dressing back down as best he could. With a bit of luck it won't start bleeding again, but luck has not been his strong point lately. He flexes his fingers.

Yes, now it really does sting. He glances resentfully at Sherlock, who is already gazing off into the distance, John forgotten.

John gets up and pokes around the VIP lounge. The curtains are stapled to the ceiling and floor, he realises. Purely decorative. Of course, but something seems off. How are they cleaned?

Why does he care?

He doesn't. It is just a habit, acquired through long association with Sherlock and his constantly wondering mind.

He tugs on the curtain and it doesn't move. Works his way along the back wall, frowning.

Sherlock is on his feet too, leaning against the viewing wall, looking at the dance floor. He has his hands pressed to the sloping glass, fingers splayed. John rolls his eyes. No more drops from a great height, please. "Too mundane," mutters Sherlock.

He presses his forehead to the glass. "Mycroft, Echelon, Americans. But we don't have Crash. We need him. Both of them. And the connection to this place." He bangs his head on the glass with a hollow clang.

John finds a place on the back wall where the curtain moves. Aha. This must be where they detach it for cleaning. His hand throbs and he curses Sherlock for fiddling with the dressing.

"So," he says. "This, this data or whatever. I'm just going to walk round with this on me, for the next fifty years?"

Sherlock's head snaps up.

"Is this just... on me... for the rest of my life?" John asks.

I stop dead. Of course. The degradation process. Or rather, the lack thereof.

I have never considered any long term effects. I expect this is because neither had Mycroft. He accepted the Hands' methods, assuming he has been aware of them - must reluctantly give him the benefit of the doubt. They have been prepared to harvest from living or dead tissue, and frankly, once the subject has smuggled their data, probably unknowingly, what use is that subject to them?

So either the Hands planned to kill every smuggler - which would soon become unwieldy and impractical - or they were just going to leave the DNA in place, and collect when convenient.

The collection is not time critical.

But the data is, potentially, time critical. And then the delivery method makes no sense.

"That's it," I says to John, and see his look of horror and confusion. "No," I add, realising that I am answering my own question and not his. "I mean, I don't know. That's not what I mean."

I am stammering. Failing completely to reassure him, but that will have to wait. He will understand.

Mycroft would never invent a delivery method which involved leaving a trace. Impossible to imagine. The marker pens - they must be the clumsy re-use, by the Hands, of an existing technology, some alternative for people with a phobia of needles, perhaps. A way to test the solution. To test that it was carrying the DNA data.

The solution...

This human testing, this business with the marker pens: this is purely the Hands.

I feel giant relief at this. I hoped Mycroft would not be so stupid as to become involved in anything so sordid. No: Mycroft has only been so stupid as to trust Crash, a mistake I never made, and now he has lost control. Crash has seen, of course, the enormous potential of this idea, and run with it. In his twisted way, he has improved it, carried out broad tests, made it scalable. It would be admirable if it were not for all the murder.

Mycroft has used me to get inside the organisation, and to get proof of the data theft. That is to say, to pin blame for the theft on someone other than the actual thief, in other words, him. With this he can sell out the Hands and close down the operation.

He is still responsible for sponsoring the development of technology which has killed many people. I expect even as I stand here, that all records of this are being destroyed.

Mycroft would be horrified to learn that the data might be permanent. But - a new hope - I expect he has never even contemplated it. He does not have a human, a normal person, a John, to point out the real cost of his actions. And that will be his downfall, his Achilles heel, even as he maintains that John is mine.

John says, "Forget it. Sherlock, there's a crack here, looks like a door."

I turn to him. He is standing in the corner of the room, running his hands along the velvet curtains. He has found a door. Probably a fire exit. My eyes travel past him to the bar, and those unusual optics. "That's it!" I exclaim.

He looks pleased, then realises I am not talking about the curtains.

Before I can explain we hear a noise.

Voices downstairs, and sounds of several pairs of feet.

"You were hoping Crash would turn up," John says, wrenching back the curtain to reveal a fine crack in the door.

I am beside him, pressing the edges, trying to work out how it opens, as footsteps ring on the iron spiral staircase up to the VIP gallery.

"No pressure," says John.

"Brilliant!" I say, and stamp the floor. The pressure sensor triggers and the door springs open. "After you," I say, and we hustle through, slamming it behind us as Crash and his minions burst into the gallery.