The Macdonalds' living room in Aberdeen. It is night time, but all the lights in the room are on, and so is the gas fire in front of the boarded-up fireplace. Someone has pushed the clutter of children's toys aside on the carpet to make a lane from the door to the corner with the sofas and armchairs. The decorations from last week's birthday party are still in place. The only new addition to the furniture is a drying rack, one half of it occupied by tea towels and toddlers' bibs, the other half by the damp remains of Joseph Bell's Landranger map, carefully secured with clothes-pegs.

On the larger sofa, John is sitting, with his bad leg propped up on the coffee table, comfortably cushioned. The leg of his jeans is rolled up, revealing a neat brace that encases his injured knee. His hair is dry, and he is in dry clothes, too – a fresh shirt, and the woollen oatmeal jumper over it. His face is grey with fatigue, but it has lost the blueish pallor of hypothermia. In fact, he looks a lot better already than he himself would probably have predicted, after his ordeal in the hills. Both a mug of tea and a tumbler of whisky are within reach on the table in front of him. He has a thick folder on his lap, and is flicking through it.

In the armchair at right angles to John sits Mycroft, still in the same suit that he wore to John and Sherlock's - only partially successful - rescue. He has his chin propped on his folded hands and is staring thoughtfully into the fire. If he has been offered anything to drink, he has declined it.

After a moment, John, turning pages, reaches a section of the file with photographs in it. He pulls a face, turns another page, then grimaces even more strongly. Mycroft glances across at him over his folded hands. He is outwardly calm, but his hunched shoulders betray his tension and his discomfort. John looks up.

JOHN (grimly): Don't let him see those pictures. Ever. He'll strangle you with his bare hands.

Mycroft smiles humourlessly.

MYCROFT: I've had two full weeks to prepare myself mentally for that eventuality, John. But thank you anyway for the warning.

John snorts, and slowly works his way back through the pictures of the crime scene. He tilts the folder to make them catch the light better.

JOHN: Yep, that is chloracne all right. At least when you know what to look for. (Looking across at Mycroft again) So that's why the autopsy report is missing?

Mycroft shrugs, but doesn't deny it. John shakes his head, and goes back to his reading, shifting his hurting leg with a low groan. Mycroft regards him with an unreadable expression, his lips pressed tightly together. Then suddenly, there are footsteps outside, the door to the room opens, and there stands MacDee, his phone in his hand, deep dark rings under his eyes but a happy smile on his face. John and Mycroft both look up immediately, and both their faces brighten even before MacDee can speak.

MACDEE: We've got him. (To Mycroft) I think you can stand your people down now, and return the helicopter, too. I've already called back my men, and the mountain rescue volunteers.

Mycroft nods appreciatively, and takes out his phone.

JOHN (putting the file aside): Where is he now?

MACDEE (smiling again): In good hands, John. A sheep farmer in the lower Glen an t-Slugain has just been knocked up by an unexpected late-night visitor, who looked somewhat the worse for wear but asked very politely for a lift back to Braemar. The man called 999 instead, of course. Constable McGregor is on his way up there right now. They'll be here in an hour.

John heaves a huge sigh of relief.


An hour later. It is still night - the quieter half of it now, after midnight, with no traffic on the roads and complete stillness in the house. Mycroft is on his feet by the window, with his back to the room, talking quietly into his phone. John is still on the sofa, with MacDee sitting next to him now. They're looking through the case file together, John pointing at pictures, MacDee nodding.

MACDEE (amazed): And Sherlock got it just from those papers in Bell's hut that he must have got exposed to dioxin?

JOHN: Yes, and from the fact that he didn't want to see Alan Gilroy. Or rather didn't want Gilroy to see him.

MACDEE: I was wondering about that at the time, you know. Gilroy made such a point of being worried about that cancelled appointment, but when I asked him what exactly it was meant to be about, he said he didn't know himself. I found that suspicious, I admit. (He blushes.) Gilroy was actually my prime suspect, until Neligan got caught and confessed. I couldn't shake off the feeling that there was something Gilroy wasn't telling me.

JOHN: You didn't tell us that, last night.

MACDEE (guiltily): I know. But once we had Neligan, I just figured that I'd been seeing things, and kind of forgot about it.

John nods. MacDee turns another page or two of the file, and jerks his chin at another picture.

MACDEE: And that notebook. (He shakes his head.) Birds' eggs in February. How could I not see that?

JOHN (sympathetically): I know. It always seems so simple, afterwards.

They exchange a long-suffering look.

MACDEE (closing the file and putting it down on the table): And so someone killed Bell for finding out about the dioxin? (John nods.) But we still don't know who that someone is?

JOHN (raising his eyes to look across at Mycroft, grimly): At least we know now why we don't know.

MacDee follows John's eyes, and raises his eyebrows in an eloquent manner.

MACDEE (under his breath): But he can't or won't rat on them?

JOHN (with very little warmth in his voice): Let's hope it's just that.

There is an uncomfortable silence.

MACDEE (awkwardly): So - (He nods at John's knee.) How's it feeling now?

JOHN: Better. Going by the x-ray, I was lucky. So fine, yeah.

He takes a sip of his tea, then a sip of his whisky, and falls back into a gloomy silence, his brows drawn together.

MACDEE (in an encouraging tone): He'll be fine, too, John.

JOHN (with a sigh): I wish I could be sure. (Managing a weak smile) Thank you, though. For looking after us, I mean.

MACDEE (chuckling quietly): Pure self-preservation. Greg would have my hide. (John smiles, a true smile this time.) But you did give me a fright, when you didn't come back from Ben Avon all day, and I called and they told me you'd never even been there. Your phones were forever "currently unavailable", and then he (jerking his head at Mycroft, who has finished speaking but is now typing on his phone) turned up on my doorstep. I wonder who will be next?

JOHN (glancing at his watch): McGregor and his charge, I hope. (With a faint grin) He'll be gloating that we needed a mountain rescue after all. Just what he was expecting.

MACDEE: Yeah, by the way – I could just have asked him to let you have the keys, no trouble.

John nods again, but he is avoiding MacDee's eyes this time. Mycroft half-turns and shoots John a quick glance. His lip curls in a knowing little smile, but MacDee misses it, because right at this moment, there is the sound of a car approaching and then stopping in the street outside, followed by a knock on the front door of the house. MacDee jumps up and hurries to open it. John - perforce - and Mycroft - by choice - stay where they are, but both their faces turn expectantly towards the door. There is the sound of footsteps in the hall, and then Sherlock and Constable McGregor, with MacDee behind them, appear in the open door of the living room.

Sherlock looks, there is no other word for it, like death warmed over. He seems to have been given a towel somewhere along his way back here to provisionally dry his face and his hair, making the latter stand on end. He has a borrowed high-vis police jacket draped over his shoulders in place of his coat, but the rest of him is still sopping wet, and splashed with mud all over - jacket, shirt, scarf, trousers, everything right down to his bare feet. He is carrying his shoes - or rather their barely recognisable ruins - in his hand. His face is ghost-like, so pale that the skin looks translucent, and his eyes, blinking into the bright light of the living room, are red and puffy like a rabbit's.

There is a moment of utter silence while both John and Mycroft stare at the pitiful figure of their friend and brother, and Sherlock seems to be looking everywhere in the room except at them. Then Constable McGregor, who looks more amused than anything, breaks it by patting Sherlock on the back with his big hand, almost making his knees buckle.

McGREGOR (jovially): Well, here we are then. Not quite the airport, nor your London office, but close enough, I s'pose. (He chuckles. To John) Didn't I tell you not to underestimate the Cairngorms? (He jerks his head at Sherlock) But he wouldn't listen, would he? Never does, I'm guessing. Well. He was lucky though that Farmer Ross grabbed his phone and not his shotgun when he came knocking. (Chuckling again) Ross and his wife thought that Ben Avon must be missing another patient, and that he was standing right on their doorstep.

MYCROFT (in a deceptively conversational tone): Interesting, Constable. How did you convince them that it wasn't the case?

McGREGOR (with an amused look at John): Told them they didn't come in pairs. Nor in Audi TTs neither. (Turning back to MacDee, in a more official tone) Right, sir, I s'pose I'm done here?

MACDEE: Yes, thank you, McGregor. I'll be in touch tomorrow.

Sherlock, who has listened to the entire exchange with a blank expression, as if it went right over his head, now comes to life, and shrugs out of McGregor's jacket. He hands it to the policeman with a nod of thanks, and McGregor responds with an indulgent, almost paternal smile. Then the constable nods to John and Mycroft, formally salutes MacDee, and walks out of the room, closing the door behind him. When he is gone, Mycroft clears his throat, and asks the only question that really matters at this moment.

MYCROFT (to Sherlock): Where's your coat?

Sherlock raises his head and meets his brother's eyes. His brow furrows, as if it costs him a great effort to process the question and arrive at the correct answer. Then he snaps out a single word.

SHERLOCK: Wet.

He lets go of the muddy shoes he has been holding, and they crash to the floor, coming to rest with their undersides turned up to the light. Both soles are completely worn through, with a gaping hole in each. And then Sherlock's knees buckle in earnest, and MacDee's quick strong arms around him are the only things that keep him from joining his shoes on the carpet.