"A man in a desert can hold absence in his cupped hands knowing it is something that feeds him more than water. There is a plant he knows of near El Taj, whose heart, if one cuts it out, is replaced with a fluid containing herbal goodness. Every morning one can drink the liquid the amount of a missing heart." The English Patient by Michael Ondaatje

John H Watson is a man of habit. Regularity and precision are as much as part of him as the beat of his perfectly articulated heart, as the one splash (never two) of the same cologne he has worn each day since his father took him aside and taught him to shave. He prepares his coffee in the same way each morning, with the same rounded spoonful of sugar from the silverware set he inherited from his mother and jealously guarded from Sherlock's most caustic experiments. The mundane and the extraordinary do not war within him but cohabit, carefully, sit shelved together like honey and nitric acid in the kitchen cabinet at 221B. It is not a precarious existence as much as a measured one, doling out equal doses of comfort and killing, of frenzy and rest. He has never regretted this battlefield of regularity and mania he has chosen so willingly. Except when Sherlock left.

Suddenly the anchor broke free of the harbor and he was left adrift, with only his heirloom spoons and his cup of coffee one sugar black and the terrible, haunted silence of the flat they had shared. A text message from a phone now at the bottom of a waterfall with its owner's hand still poised over the 'SEND' button. A less-than-160-characters love letter from a man he had loved so gently-wildly, with such carefulness and ferocity, that it had broken him and left him still, a ticking clock without a minute hand, without anything but endless days of empty. So he is left to do what he must. Carry on.

He walks the same paths that were once lit up with mystery, so nuanced and rich, where every scrap of trash held an entire universe of data, data, data. No more. Now London is just London, dirty and dreary and dark and cold, always cold. He walks the paths to the bars and to the clinic and sometimes to Sarah's, but never to Barts. (That is a scab that might never heal, and to pick at it will only let the infection in. He keeps that one covered up.) The joy is drained from these endeavors, but so is it from much of the world now, now that it has been emptied of its most precious, its most rare possession. The man who could see beyond its crust and into the core of all its evils. He tries not to notice.

The nightmares return. Now there are more of them, watery monstrosities mixed with the searing heat of the desert, Afghanistan and Reichenbach dredging together to create a silky, sweaty sediment, trapping him under sand and sea and the dead weight of all the people he had loved and lost, most of all Sherlock clinging so strongly to him, wetting him with his blood and tears. He isn't sure what is worse: the nightmares or waking up alone, knowing the dream is not far from reality. No long lithe form stretched catlike over the bed beside him, for him to run his fingers over, mutter the names of the muscles he touches, and see those lush lips light up in a smile, even in sleep. Nothing but the ceiling, cracked and discolored from nearly a century of service, the light with its bleary opacity, the window buffed within an inch of its life. Everything of transport and nothing of substance.

And the limp is no better now, psychosomatic origin be damned. He is certain that something happened at the pool, some twist in the tendon or infarction in the muscle, so slight to be unseen but devastating. Some days he can barely walk, so he remains confined to his room, brooding. He calls off sick from the clinic. Sarah's calls become less and less frequent, colder. London seems to be growing colder too. There is hoarfrost settling in, in his heart, on his bones, and there is nothing left to warm it.

By chance he happens upon it. He's home one day, begging off work again, when Mrs. Hudson bustles in and asks if he could take a peek at the gutters. They're all clogged up and her hip won't take well to perching on a ladder and with just the two of them in the whole building, it just doesn't seem right to call for a repairman. He can't say no, not when she's been so understanding about a few missed payments, slipped banana bread into the fridge when he forgets to eat and lends him some firewood when his leg practically gives out. And the pneumonia he fell to soon after Sherlock left. (Left – he refuses to say died. Not that finality. Not yet.)

He climbs up, stopping twice to wince and rub his leg. It's cold, the wind whipping smartly along the rooftops: fast enough to sting his face, but not to unseat him from the rickety old ladder. Green ladder. He wants to laugh, remembering the first text Sherlock sent from his phone, but the noise won't come and he merely sounds like he's choking. The wind coaxes a tear from his eye and he wipes it away impatiently. No sense crying, John Watson. Man up.

The gutter looks clean enough: some fallen leaves, a plastic bag. He pulls out the trash and lets it fall to the ground, ignoring the ripe splat as it lands on the wet cement. A light snow has begun to fall, the kind that freckles the ground but does not last, as it has not yet cooled enough for it to stick. It will melt and run off, forgotten. He wonders idly why the snow even bothers, in weather like this. A futile gesture of winter, the first firefight of the two seasons locking antlers. He sighs.

Atop the roof someone has left a telescope. Curious, he hefts his weight full onto the roof, praying that he doesn't go crashing into the attic. The tiles are strong enough to hold him, their traction adequate for his heavy boots. A thin path has been worn into them, as if someone came here often. Like a tightrope walker on his favorite wire. Unconsciously he begins to deduce what he can from the tread of the shoes, from the lightest feathering at the edges. At least Sherlock taught him something in their time together. But he knows he doesn't have to guess who it might have been.

The telescope is covered with a black trash bag to keep out the moisture. It hasn't been calibrated in at least three months now, its markings of the night sky engraved along the edges are sure to be far off, and he doesn't know enough to fix them when the stars come out. His heart drops when he realizes what it means, and the wind seems to whip harder, tearing more tears out of his eyes.

Sherlock kept the stars for him when he was there. He taught himself the solar system because John said it was important. He sacrificed the space in his brain, the precious memory on his hard drive, because John said stars mattered. Inside the trash bag are some books on the night sky around London. Light pollution would render most of it unintelligible – not even Sherlock's keen eyes could cut through all that glare to see up at the cosmos – but he imagine the man would have tried. He came up there every night, or almost every night. That much was clear from the weathering on the roof tiles. All because of an offhand comment on his blog. John himself doesn't know a damn thing about the constellations other than the basics that he'd been taught in school, but somehow it became important to his flatmate, important enough to climb up on the roof every night and pore over the books of the night sky and peer unsuccessfully into the telescope to unfold the universe.

He climbs up there every night now. A few weeks in Mrs. Hudson makes excuses and has a widow's walk constructed, saying she had meant to for years, but John knows she's lying. (The name seems oddly appropriate to him, for they are two widows in a sense, though he'd never say so out loud.) A few weeks after that a sturdier ladder appears. John installs a chair and a little plastic awning to keep the snow from the telescope, and he brings a thermos up with him, sipping at it and rubbing his leg and looking out into the sky.

It becomes a ritual like the spoons and the coffee and the cologne, just another habit in his pantheon of comfort routines, just another thing to hold him from slipping off the earth and falling into oblivion. He sits in the cold, wrapped in a blanket when it's nearly too much to bear, and he reads about the stars. When Sherlock returns he'll tell him about Orion and Andromeda and all the others. And if he doesn't return – if he's gone forever – then John will keep climbing each night until he can't. Until then he follows the cycles of the moon, he squints through the telescope into the blankness and looks for anything he can see: he keeps the stars.

He keeps the stars because it's the only thing left to keep.