John woke to the distant rushing and rumblings of London in the pre-dawn. He was warm, safe, comfortable, and supremely content; Sherlock lay draped over him, lanky white limbs enveloping him possessively as he slept. John had somehow tangled his fingers in the wild curls – a delightfully unexpected discovery – and slowly, idly, he caressed Sherlock as he had always longed to be able to do.

300 years ago it had been an unspoken thing between them. The others had known of it – there had been few secrets among such a tight-knit band – but they had thought it best to be discreet, hoping to avoid Moriarty's attention, for the Brigadier had always reacted viciously to any hint of a rival influence over his favourite protégé.

But Moriarty was dead, and the wars and the desert were centuries in the past: here and now, in the 23rd century and in the privacy of their own flat, they could do whatever they pleased.

"What are you thinking?" Sherlock mumbled, arching into John's gentle scratching like a great, lazy cat. John abandoned the tangled curls and stroked his hand over Sherlock's back and shoulders, feeling warm, smooth skin, lean muscle, and the coiled potential of genetically engineered strength.

"I never truly believed we'd ever have this," John said, remembering hurried fumbling in the dark, rare moments of privacy snatched between engagements.

Sherlock hummed slowly, looked up at John with his eerie, all-seeing eyes. "And is it everything you imagined?"

John knew that Sherlock did not merely refer to their shared bedroom and the freedom to finally touch and be touched. Sherlock's question also encompassed the cluttered eccentricity of their flat, the surrounds and environs of London itself, and the blend of mundanity and crazy excitement that was their new life.

"God, yes," John said, meaning it with all his heart.

Sherlock's comm beeped, interrupting the hushed silence. He scrambled up in a flurry of limbs and clambered over John to the bedside table, reading the message with a hum of pleased excitement. "Lestrade," he said, eyes gleaming bright. "Come on, John – we've got a case!"

Federation security officer Lestrade, based at what had once been New Scotland Yard, had grey hair, tired, shrewd eyes, and enough flexibility (and sense of humour) to have at least listened to Sherlock's proposal when had first offered his assistance. John had liked him on sight; Sherlock, a harsher critic, had said that he was not entirely a fool.

If Lestrade had looked at Sherlock's quite distinctive features and connected them with the destruction of a Starfleet archive and the subsequent manhunt, he made no mention of it; John suspected that he had made the connection, looked into it, and had been kidnapped by a man with an umbrella.

Whatever Lestrade's reasons, he called Sherlock in for baffling and inexplicable cases, wearily tolerated Sherlock's abuse, stopped his team from abusing Sherlock in turn, and accepted without – much – question his pronouncements and conclusions.

Of such things were new beginnings born.

Now Lestrade waited for them at a luxurious, refurbished Victorian home, where a woman and two men lay dead in their own parlour, their faces contorted with madness and terror.

"Owen, George and Brenda Tregennis," Lestrade said, "all siblings. Their brother, Mortimer, found them this morning. All the doors and windows were shut, and there was no sign of a break in or forced entry."

John watched as Sherlock examined the room, peering here and there with his magnifying glass, sniffing at the air, and leaning in to check the old-fashioned oil lamps and the ash in the fireplace. John thought he could detect a faint, lingering scent that raised the hackles on the back of his neck, but with the windows now open it was almost gone.

"Oh, it's beautiful, John," Sherlock crowed, grinning wickedly. "A weaponised hallucinogenic poison, it must have been – sprayed, or more likely burned, given the fireplace. It must have been exotic, not one of the commoner poisons, or they would have smelled it; Dimoran bloodweed, perhaps, or the blue mountain daisies of Tau Ceti Beta –"

"Hang on," Lestrade interrupted, although quietly, so the rest of his team could not hear, "how do you know so much about weaponised hallucinogens, or xeno-poisons?"

Sherlock stopped, turned to face him, and for a heartstopping instant John saw Khan looking out of Sherlock's eyes, before the familiar mask of exasperation dropped into place. "Really, Lestrade, I could hardly call myself an expert in my chosen field if I focused only on Terra-centric ways and means. Or do you think criminal behaviour is confined only to humans? There have been some wonderfully ingenious alien murderers."

Lestrade flicked a glance to John, who only shrugged.

Sherlock continued. "You're looking for someone with an extensive knowledge of esoteric xeno-biology, and a fascination with the exotic and the macabre –"

John avoided Lestrade's ironic eye.

Just then the call came in that Mortimer Tregennis had been found, horribly murdered exactly like his sister and two brothers, and Sherlock laughed delightedly. He gathered up his coat, threw his scarf around his neck, and whirled out of the room with nothing more than a "Come on, John!"

John followed, as he had always followed, from the very first time he'd met the brilliant, fascinating force of nature that was Khan Noonien Singh.

Long, frantic, terrifying and exhilarating hours later, after Sherlock had nearly poisoned himself, after they'd finally unravelled the puzzle and apprehended the culprit (Brenda's secret lover, a xeno-biologist, had unwittingly told Mortimer Tregennis of Andorian devil's foot root, thus providing Mortimer with the perfect way to gain control of his family's mining empire; the xeno-biologist, driven mad by grief, had poisoned Mortimer in turn) Sherlock and John found themselves back at 221b, high on the successful completion of a delightful case.

They slumped down on the couch, pleasantly exhausted, and very proud of themselves; John looking at Sherlock in admiration, and Sherlock looking at him as though he had been gifted with a marvellous puzzle. He had always looked at John like this, even in the desert; John had never been able to work out why. Khan and his men had hardly needed a field medic, especially one pushing 40 who, for all his fitness and experience, had barely been able to keep up with their enhanced stamina. But Khan had always marvelled at the simple things: common sense; steady hands; John's ability to turn his hand to most things well, rather than some things brilliantly.

"You're the steadiest and most competent man I know, John," Sherlock said suddenly, breaking into John's thoughts as he sometimes did with uncanny insight. "When I woke without you and realised 300 years had passed, that everything I had known was gone, I didn't know what to do. I only knew that you could have guided me, but Marcus refused to awaken you. I had to find my way for myself."

John winced. But what was done was done, and John had always known that Khan was dangerous; he had simply refused to believe it was all Khan could ever be.

"You seem to have adapted well enough," John teased, trying to lighten the mood. "You certainly know your way around this new London. I'm still trying to unravel the technology –"

"Technology is nothing," Sherlock said, tangling a hand in John's hair and drawing him in, until their brows pressed against each other's and all John could see were those luminous eyes and all he could breathe was Sherlock. It was something John had taught Khan, in their first tentative forays into intimacy; a calming, steadying gesture, an affirmation of togetherness. "You're my moral compass."