John had asked Jacob to turn off the heat in the Land Rover a mile before the bridge, but that still doesn't prepare him for the cold.

It's brutal. The wind moans as it reverberates against the hillsides and drives snow and sleet in every direction. If it wasn't for his goggles, he'd be blinded by pellets of hail being whipped into his face.

And the storm is just getting started.

John regards the chrome and fire-red motor bike, its cover blown by blasts of icy fury knocking away the brushy camouflage, and knows he's on the right track. He draws a breath that burns its way down his lungs and then slaps the bonnet of the Land Rover, letting Jacob know that he should head back to the safety of the village.

Jacob mouths, 'Are you sure?' at him. John hesitates and then nods. He hates losing his ride, but Jacob is just a kid. He shouldn't be out on a night as savage as this one is shaping up to be, worrying his father needlessly. John isn't thrilled to be out in the weather himself, but Sherlock's been missing for hours and their quarry, an escaped prisoner who is now back in the custody of the prison authorities, isn't talking.

"This is another fine mess," John thinks as he ties the hood of his parka more securely under his chin and then unfurls his collapsible walking stick, "that you've got us into, Sherlock." Damn the man and his impulsive nature anyway. What had persuaded him that haring off on his own was a good idea? Especially when reinforcements, in the form of the prison authority, were on their way.

With a last look at the diminishing Range Rover, John squares his shoulders, switches on his torch, and begins to trudge up a road that should more accurately be called a sheep trail. His intended destination lies at the top of the long, winding track carved into the hillside. Fighting his way against a gale that threatens to suck the breath from his lungs, he prays for a less dire reason for Sherlock's disappearance than the ones he's been imagining.

A gust of wind blows him sideways, nearly taking him off his feet. He slips and skitters over rocks and ice using his walking stick as a brake. Finally he comes to a halt a bare six inches from the edge. Cautiously, he looks over the side. It's a sheer drop. At the bottom, sharp stones and gorse bushes protrude from the snow. Grateful for the heavy boots and his walking stick that allowed him to avoid a slow and probably painful death, John pushes back against the wind until he regains the centre path and begins to hike upwards once more.

Two meandering bends and too many difficult steps later bring him to the summit. Despite being in pretty fair nick, he's exhausted and has to pause to catch his breath as he surveys the terrain. There's a shack, a couple of out buildings, and a stone well with a pump handle and hanging bucket. No lights shine from the windows. No smoke curls upward from the chimney. There are no signs of activity at all.

Frowning, John approaches cautiously, easing his way around a wood pile as he reconnoitres. The place seems long abandoned, and he can't imagine what has drawn it to Sherlock's attention. Exchanging his walking stick for his pistol, he uses the cover of the storm to approach. What he sees makes the blood roar in his ears and his vision, already painfully under siege by the blizzard, dim. The windows are open, as is the front door.

"Oh God. Please no," John whispers. A scene has been staged. Just inside the hewn timber threshold there sits a high-backed chair. In the chair is Sherlock. He's been stripped naked, his head is bowed, and he's not moving.

Heedless of his own safety, John runs the remaining few feet to the doorway. He slips on the ice and comes to a skidding stop inches from Sherlock's chair. Sherlock moans and tries to smile, although his face is a bruised and bloody mess. He speaks in a voice that's barely audible. "John," he mumbles. "I knew you'd come."

Torn between relief that Sherlock's not dead and anger, John scowls in reply and then makes a visual sweep of the shack's interior as he shuts the door behind them. There's three visible windows and they all stand open. Moving swiftly, he pulls them shut and latches each securely against the weather. The hearth is empty, and the vintage Aga is cold. It's fractionally warmer without the wind howling around him, but it's still freezing. His breath hangs on the air in clouds as it condenses. Wishing he could be in multiple places at once, he yanks his mobile from his pocket, sees there's no signal, and then puts it, and his gun away. Neither one will do him much good in the coming hours.

Sherlock has been bound to the chair with both duct tape and rope. His skin is icy to the touch and he's barely breathing. However long he's been this way, it's been too long, and exposure to the cold has given way to hypothermia.

"Right." John drops his rucksack onto the floor and pulls off his stocking cap and goggles. He puts the cap on Sherlock's head and then digs into his rucksack until he finds an emergency blanket which he unfolds, slits with his knife down the centre, and then drapes over Sherlock and his chair like a poncho. The chair legs scrap across the worn wood floor as John drags it – and Sherlock – to rest closer to the fireplace. "Don't go away," he murmurs before opening the door just enough to slip outside.

Mindful of his eyes, John replaces his goggles and then trudges repeatedly between the wood pile and the front door, dumping logs into a rough stack. Five trips later, he figures he's got enough fuel to hold them until help comes, so he hefts the axe that had been left propped against a splitting stump and slides it through the barely open door before going back for a final armload of wood. He carries it inside with him and then drops next to the fireplace.

Sherlock mutters his name. John ignores him. He peels off his gloves and goggles then chops a stack of kindling – disregarding the ruin that he makes of the floor – and then assembles it into a rough pyramid over the grate in the fireplace.

He has matches and fire-starters in his kit, but the wood is damp from the snow and it's going to take an accelerant to get it going without a lot of fire tending. Fortunately, there's an old fashion oil lamp on the kitchen table. He dumps a little of the oil onto the kindling and sets a match to it. For a moment the air stinks of paraffin and then with a whoosh, the fire bursts to life. With a relieved sigh, John reassembles the lamp, lights it, and then turns his attention to Sherlock.

"Idiot," he says softly, letting go of a little bit of his frustration. "Why didn't you tell me what you were planning?"

Getting Sherlock warm has to be the first of his priorities, even before tending to the cuts and bruises that mar his face. John peels off his parka and drops it over the Mylar poncho. He considers his gloves, sitting abandoned on the table, but there's no way he can put them on without untying Sherlock's hands first, and they're too small anyway. John looks around the rough-hewn room to see what Sherlock's captors have left him to work with.

There's not much.

Now that the shack isn't shrouded in darkness, two doors become visible. One leads to a bare airing cupboard. The second to a bedroom with another opened window. The bed has been stripped to a faded striped mattress. There's a ewer and basin on the dresser next to another oil lamp. Under the bed is a chamber pot. Sherlock's clothing is nowhere to be seen. There's a telephone mounted on the wall. Lifting the receiver gets him nothing. The line has already been blown out by the storm.

He shuts the window and he then hefts the mattress off the iron bed frame and drops it in front of the fire. He glances over at Sherlock, sees that he's passed out again, and makes a decision. Rather than risk exposing him to repeated changes in temperature, it would be far better to move the stash of firewood inside all at once. He does so, as quickly as he can, fuels the nascent blaze in the fireplace, and then builds a second fire in the Aga. Only once he is sure that it has taken does he focus on Sherlock.

His jacket and the Mylar poncho are in the way. John strips Sherlock of his temporary shelter and uses the field blanket as a mattress cover. The sharp blade of the folding pocket knife makes short work of the layers of rope and tape. It only takes seconds to free Sherlock from the chair, but in the state he's in, those seconds are precious and John curses their loss.

Without his bonds, Sherlock sags forward. John catches him and half carries, half drags him onto the mattress before dumping the contents of his rucksack onto the floor.

Among the supplies are a mountaineer's first aid kit that's considerably more comprehensive than the sort most people keep, several more Mylar blankets, some concentrated food bars and bottled water, extra socks and a change of clothes for them both, something Jacob had insisted upon when he'd heard the forecasters warn that all residents should button up in preparation for the blizzard.

Sherlock groans, roused back to semi-consciousness by the warmth that's beginning to creep into the room. John drops to his knees and takes Sherlock's wrist between his fingertips. The pulse, normally so robust, is slower than normal, and weak.

"Rats and moles. Should have known he'd be tipped," Sherlock mutters before being overcome by a new wave of racking shivers.

John ponders the cryptic words as he unwraps his emergency supplies and then he thinks he gets it. Sherlock suspected someone inside the dragnet of aiding the escaped prisoner. It doesn't make him feel much better about being left behind, but he understands that if both of them had gone missing at once it might have raised a red flag. Not that any of it mattered now. What did matter was getting Sherlock's core temperature up to something approaching normal with no proper equipment. He opens all of the blankets and piles them on top of Sherlock's trembling body, follows those with his parka, and then throws another log on the fire, causing the carefully constructed stack to collapse and smoulder.

There's no tools on the hearth, not so much as a rusting poker, but whoever cleared the shack had left a ladle hanging next to the Aga. John uses it to rearrange the smoking wood before the fire smothers itself.

He drops onto a kitchen chair to take off his boots and then notices curls of black smoke seeping out of the Aga. Padding over in his stocking feet, John stares at the stove for a long moment and then realises that there's a handle on the side, some kind of vent control. He tinkers with it a bit, improving the cooker's airflow. When it seems like he won't burn down the shack an attempt to keep them warm, he returns to Sherlock.

Flames from the fireplace dance on the reflective surface of the Mylar blankets giving the illusion that the fire has leapt free of the hearth to envelop Sherlock in its warmth. If only it could be so, John thinks as he watches the bedding shimmer in time with Sherlock's shivers. Despite the two heat sources, the air temperature in the shack is still unbearably cold.

John drops to Sherlock's side, blows into his cupped palms to warm them, and lifts the blankets. He takes one of Sherlock's hands in his and rubs it vigorously for nearly a minute, tucks it carefully back underneath the blankets, and then repeats the massage with the other hand. He moves down to the end of the mattress and rubs Sherlock's feet, noting he seems to relish the contact, pressing his toes against John's palms in response to the massage.

Finally, John peels off his snow drenched trousers, folds them over the chair to dry, and slips underneath the layers of Mylar, strangling a yelp as he presses his chest against Sherlock's back. It's like cuddling up to a lanky block of ice and John can feel the heat being leached from his body by Sherlock's trembling frame. "I guess I should feel lucky, whoever did this to you left you your pants," he murmurs against the nape of Sherlock's neck. The scrap of cloth separating his genitals from Sherlock's icy bum is at least a psychological defence against frost bite.

Getting Sherlock's blood moving is paramount. Increase the flow to the extremities to prevent damage to his fingers and toes. Warm his trunk to elevate his core temperature to prevent cardiac arrest. If they were in hospital, there would be thermal blankets and warm fluids to raise Sherlock's temperature at a carefully controlled rate. There would be monitors to keep vigil over his heart rhythms and blood pressure. The rucksack contained none of those things, and wishing won't make them appear. If Sherlock is to survive the night then John must make do with what he has. He starts by shifting to a slightly less awkward position and massaging the blood outward from Sherlock's heart to his limbs.

Outside, the storm ratchets up in intensity. The howling wind sends gusts down the chimney, making the embers dance erratically. Draughts of deadly cold air seep through chinks in the crudely constructed walls. The blizzard seems like a living thing, some sort of angry nature spirit bent on vengeance. As John chafes Sherlock's too cold flesh, he wonders what they have done to earn its ire.

"John?" Sherlock murmurs.

"Yeah, it's me," John replies. He presses his lips to Sherlock's nape, gauging his temperature. "I've got you."

"John?"

"Yeah, Sherlock, I'm here."

"John," Sherlock mutters again. "Loyalty divided is no loyalty at all..."

Confusion is a symptom of hypothermia, but even so, it sounds like there's a message in Sherlock's cryptic pronouncement. As John pauses to stretch out his cramped fingers, he wonders what bearing they might have on the case.

Time passes. Sherlock's condition is improving, but it's a slow process. Fortunately, as long as his body temperature is rising, slow is good. Too rapid changes could lead to shock or organ failure, and there's no way, stranded as they are with no help forthcoming, would he survive such a catastrophic event.

Another murderous gust blows down the chimney, threatening Sherlock's progress. The fire needs feeding if it's to withstand the cold. Reluctantly, John eases out of their nest and then tucks the blankets closely around Sherlock's frame to conserve heat. He piles the remaining logs from the hearth onto the coals, and then shifts the stack by the door, stacking the wood in a neat pile near the hearth, so that it can dry out properly.

He shoves an extra log into the Aga even though it doesn't really need feeding. It's a more efficient heat source than the ill-maintained fireplace, and for a few seconds, John considers moving the mattress closer to it. Wearily, he decides that it's too much work for too little reward, and he climbs back into bed with Sherlock, this time reclining so that they are chest to chest. Once again he begins to massage Sherlock's arms and trunk, ignoring his own discomfort as he gently pummels Sherlock's still too cool skin. As he works, he tries to avoid looking at Sherlock's face.

Both eyes have been blackened. They're swollen nearly shut. Blood is crusted on his cheekbones from the sort of cuts that come from someone using coins or washers wrapped in a cloth sack as a blackjack. His upper lip is lacerated and puffed. It's hard to judge, but it may need sutures. From the looks of it, Sherlock's nose is okay, but that's got to be down to luck. A surge of heat pumps through John's veins. He realises it's anger, pure and unadulterated. If he ever catches up with Sherlock's assailant then there will be hell to pay.

"John?" Sherlock raises his chin as he once again regains consciousness. He tries to open his eyes but blood has matted his lashes together.

"Yeah, Sherlock, it's me," John replies quietly, his anger forgotten as it is overshadowed by worry. "I'm here. You're safe."

"I can't see," Sherlock mutters querulously. "Why can't I see?"

"You've been hurt," John says matter of factly. "You must have been your usual charming self, because someone's used your face as a punch bag." He teases gently, knowing Sherlock will take comfort from the rebuke. "I need to clean the blood out of your eyes, but we need to concentrate on warming you up for a little while longer. Okay? I know it's hard, but I need you to be patient."

"Warm is good." Sherlock snuggles against John, frowning as he feels the wool barrier between them. "Why are you wearing a jumper in bed?"

"I forgot my pyjamas," John replies as he wraps his arms around Sherlock's shoulders and gathers him in close.

"Mycroft never let me forget my pyjamas," Sherlock mutters. "He always … looked out for … me. Brothers … do that."

"Yeah, of course they do." John keeps his tone agreeable, even though he has dark thoughts about the way Mycroft has carried out his brotherly responsibilities.

"Even brothers that aren't blood." Sherlock slurs his words as if he's drunk. And he's just as adamant as if he'd had a skin-full, poking John's shoulder repeatedly for emphasis. "Sanchez counted on that. ... Needed help. … Went to his … big brother."

Gradually, the nonsensical mutterings give way to soft sighs as Sherlock drifts to sleep. John listens to the wind howl and the ice clatter against the windows and tries to put the pieces together. As far as he remembers, there was nothing in Sanchez's packet about a brother, and they certainly haven't run across anyone with that surname since they'd arrived in Rockmere.

After a while, John disentangles from Sherlock's embrace, checks his vital signs, and breathes a sigh of relief at the general degree of improvement. Though the lamp-lit shack is hardly an ideal clinical environment, Sherlock's wounds still need tending. He breaks out the first aid kit and gets to work, using saline and cotton gauze to wash away the dried blood from Sherlock's face before scooping some snow from the bedroom window sill to make a cold compress to take down the swelling from his eyes and mouth.

"Somebody didn't like you crashing their party," John mutters as he applies a series of tape strips to the cut over Sherlock's left eye. He surveys his handiwork and gives a nod of approval. He moves on to inspect and dress the bruises and abrasions on Sherlock's wrists, and then conducts a general assessment, finding to his relief that there are no broken bones or contused organs to worry about. Satisfied that he can do nothing more, he eases a thermal shirt over Sherlock's head and puts a pair of socks on his feet. Dressing properly can wait until morning.

Even though the shack has finally become comfortably warm, the fires need stoking. As he fiddles with the Aga, John realises the night is catching up with him. He takes a few minutes to tend to his own needs, eating one of the energy bars and drinking a bottle of water. Fatigue washes over him as heavy as the cold had earlier and he yawns, wishing for a cup of strong tea or even better, a cup of coffee. But neither he nor Jacob had thought to include a mess kit amongst his hastily assembled supplies, and the kitchen cupboard is bare of pots and pans.

Sherlock stirs. With a groan of pain he gingerly touches his cheek and then tries to sits up.

"John?"

Instantly, John is on his feet and at Sherlock's side. He puts an arm around Sherlock's shoulders to support his weight, and smiles. "Hey, there. Take it easy, you've had quite a night."

Sherlock smiles back, obviously chagrined. "Not quite the one I'd planned. How did you find me?"

"Jacob is a gadget freak. His motorbike, the one you took?" John prompts just in case Sherlock had forgot that part of his adventure. "It's fitted with GPS tracking. We just followed the signal on Jacob's mobile and hoped for the best."

"Sanchez and Morrison?" Sherlock asks, concerned as always about whether the details of the case fit his theories.

"Morrison?" John echoes, surprised. The only Morrisons he knew of were Jacob and his father. He wonders about the call, allegedly from an elderly neighbour, that had sent the older man out of the inn at a run.

"Foster brothers," Sherlock says before his eyes close and his tentative hold on consciousness slips. Once again his body's need for rest has outweighed his compulsion to explain.

"Foster … " John mouths and then shakes his head. No doubt when Sherlock is more himself, he'll explain the chain of details that let to his epiphany. Until then, he'll just have to puzzle out the connections for himself. Unfortunately, it's a long way until morning and he has plenty of time to think.