A/N: Wrote this in one sitting and it's unbeta'd so any and all mistakes are mine. It was going to be a prompt fill but turned into something entirely different. So enjoy my first Khanolly/Sherlolly crossover-type fic with Sherlock as well as Khan in the story. Warnings for dubcon, in the sense that...well, you'll see. As always nothing belongs to me but the plot and the dialogue, enjoy!

He told himself he was being unselfish. Giving her – giving them – what they most wanted but were unable to have: a child. The genetic defect was easily correctable, if Earth wasn't so ridiculously terrified of the so-called 'evils' of genetic engineering. Oh, a certain amount of corrective gene manipulation was allowed, of course; no child ever needed to suffer through birth defects, no adult needed to be crippled for life by degenerative muscular disorders and the like. There was no ban on genetic intervention for life-threatening medical emergencies – but there was no leeway given beyond that, not even for quality-of-life issues. The scars the Eugenics Wars had caused were deep and far-reaching, not yet healed despite the passage of three centuries.

Infertility, it went without saying, was not a life-threatening medical emergency. People could adopt, they could use surrogates and host-mothers, they could go for non-proscribed medical treatments such as IVF. Human infertility in general had been long since vanquished, as medications and surgical treatments became more and more sophisticated, as contact with alien species and alien worlds had dramatically increased Earth's knowledge and access to different technologies and different pharmaceuticals.

The single exception was if there was a genetic defect uncorrectable by conventional methods. If

a woman or the man she wished to father her children needed genetic intervention to allow them to conceive, they either resigned themselves to their situation or were forced to seek illegal assistance off-planet, risking severe legal and social penalties.

And for those whose bloodlines carried the taint of Augmented genes, no matter how watered down, no matter how infinitesimal, the penalties were even more severe than for the general populace.

Which was why he found himself here, today, occupying a chair in the sitting room of a flat in London that did not belong to him. Waiting for a woman who also did not belong to him, but was the wife of the flat's owner. A man who was descended from him, a true product of the 24th century as he himself was not and never would be.

Not when he'd been awakened into that century and bound into service to a man whose craving for power rivaled – no, surpassed surely was the more accurate word – any he'd ever been personally credited with having.

Khan's lip curled as he sat in the dimness of the early evening, thinking of Admiral Marcus and how very, very much he would like to kill that man. He was the head of the clandestine Starfleet agency known only as Section 31; he was the man behind those who perpetuated and actively encouraged the myth that genetic experimentation was one of the worst evils to befall mankind since the snake slithered into the Garden of Eden (not that most humans believed in such things these days, but religion was not entirely unknown and the Fall of Man was a legend vividly recalled). He was the man who would not hesitate to put a stop to this plan of Khan's should he ever find out about it.

He was also a man who had severely underestimated his opponent. Believing that one held the upper hand often made one complacent, and now that Marcus believed 'John Harrison' to be completely in his thrall, controlled and somewhat cowed by the threats to his still-sleeping crew, he'd started making mistakes. Small mistakes, but mistakes nonetheless.

Mistakes such as allowing Commander Harrison the same freedoms – on Earth and only on Earth – that any real Starfleet officer had. Such as the freedom to live in his own flat, here in London, when he was off-duty. As long as 'John Harrison' continued to do Marcus' bidding and build bigger and better weapons, to design the warship the Admiral wished to become the flagship of an armada to be taken into war against the Klingons, then he was allowed to do as he wished in his free time.

He was not entirely free of surveillance, of course; Marcus wasn't stupid, after all. But as long as Khan stayed away from spaceports and government facilities, as long as he made no attempts to communicate with those who might see Marcus' grand vision as nothing but the twisted obsession of a fanatic – which, of course, was exactly what it was – then 'John Harrison' could spend his few off-duty hours as he pleased.

Marcus' surveillance of him wasn't what was stopping him, of course. If he thought going to the Earth government or revealing Marcus' plans to Starfleet would get him what he wanted – himself and his crew off Earth, on their way to a world they could colonize and live in peace on far from the Federation – then he would have long since found a way to do so. But he knew that a man who had been condemned to death three hundred years ago as a war criminal would hardly merit their mercy, even in this so-called 'enlightened' era. And Marcus no doubt had backup plans in place for just such an attempt, in the encrypted maze that was Section 31's securest files. The ones Khan himself had been unable to create an algorithm to decrypt as of yet.

No, he'd long since written off humanity in general as a lost cause, and very little he'd seen since being pulled from his cryotube had given him cause to alter that opinion. Yes, they'd united and reached for the stars, but only after centuries of almost unceasing warfare after the Augments futile attempts to end that vicious cycle had finally ended in ignominious defeat, Rome falling before the barbarian hordes. No matter that Earth was now part of a union including hundreds of other worlds and species; for all their accomplishments humanity remained at heart the same petty, self-involved sheep they'd always been.

The few exceptions he'd found had only served to reinforce his views on the bulk of humanity: the sheep didn't want to know how the meadow was kept safe, as long as it was. Leaving Admiral Marcus and Section 31 to act as the wolves they were with little fear of discovery.

The woman he was currently awaiting wasn't one of the sheep. Nor was her husband. He credited their Augment ancestors, the woman's unknown, but the man…Ah, yes, the man. Khan smiled and steepled his fingers beneath his chin, adopting a pose he'd seen the man use on numerous occasions, since he'd started his clandestine surveillance of the pair and their closest friends.

He'd timed this visit perfectly; the man, his own descendent as covert genetic research had proven, was headed off Earth to follow up on a lead for his current case – or so he believed. Mr. Sherlock Holmes was a renowned criminal investigator, a self-styled 'consulting detective' who was very much in demand both on and off Earth. Khan had researched the man's life quite thoroughly, wanting to know everything he could learn about his descendent. Discovering a way to manipulate him into leaving Earth for at least two weeks had been child's play, leaving Khan to further his personal plans for the man and his wife. The two of them, Sherlock Holmes and Dr. Molly Hooper-Holmes, were based in London, where she worked as a pathologist at the renowned St. Bartholomew's Hospital.

He'd researched her just as carefully as he had his descendent, and knew that Molly's shift had ended an hour ago. She disdained the use of public transporters for short-distance trips, and would instead of have taken the 24th century version of the Tube home. She should be arriving any minute…ah, yes. There it was; his superior hearing picked up the sound of the front door opening, the soft murmur of voices as Molly spoke to the landlady, Mrs. Hudson, before the light tread of her feet sounded on the stairs.

Khan smiled to himself. He wasn't a selfless man; he wasn't doing this just for the sake of a childless couple getting the one thing they most wanted and seemed destined never to have. No, he was doing this for himself as well. To continue his legacy, to leave behind a positive deed to perhaps compensate for the storms yet to come. Because no matter how cleverly Marcus had hidden his seventy-two sleeping crewmembers, Khan knew he would get them back. And in doing so, blood would unquestionably be spilled.

And also, he conceded to himself as the door to the flat opened, because from the moment he'd first seen Molly Hooper-Holmes' image on his computer screen, he'd known he wanted her.

oOo

Molly walked up the stairs to the flat she and her husband of five years shared. She'd wanted something bigger, of course, once they decided to have children, but that dream was long since shattered, and 221B Baker Street was just fine for the two of them.

She pushed aside the pain that always clenched in her gut whenever she thought about children. Sherlock hadn't been terribly enthusiastic when she'd first broached the subject, but had changed his mind in that way he had, when he would immerse himself in his mind palace in order to explore every aspect of some new idea he'd been presented with. Especially new ideas that had literally never occurred to him; Molly had been stunned that he'd never believed she would want him to father children with her. Then again, he'd also been stunned when she'd fallen in love with him, and when she'd proposed. Just as he'd been stunned when he realized that John Watson considered him not only a friend, but his best friend. And when he'd asked Sherlock to be best man at his wedding to Mary…God, had it been seven years already? Yes it had. Seven years. Isabelle was six, and little Robbie was three.

There it was again, the clench of pain, like a fist in her gut. She was happy for her friends, she really was, but it hurt, knowing that she and Sherlock would never have their own children. Not unless the ban on genetic engineering was lifted. Or if they wanted to live on the outer fringes of the Federation, on some unaffiliated planet where Molly's genetic defect could be illegally corrected.

No, stop it, Molly, she ordered herself crossly as she reached the hall. That way leads madness and you already know it. Sherlock had cautiously broached the subject with her once her diagnosis had been confirmed, and she'd absolutely nixed the idea. She wasn't suited for the life of a fugitive, and it would kill Sherlock to have to leave Earth for an extended period of time again, as he had during the whole Moriarty mess. Those two years had been hell on both of them, but at least it had served to not only clear her husband's name and erase a menace to the planet, but also to help clarify his feelings toward her. Knowing that he loved her had gone a long way toward easing the sting of the separation Moriarty's evil plans had forced on them.

With a sigh and a shake of her head at her melancholy thoughts, she entered the code that would unlock the door, then pushed it open.

She'd shrugged out of her coat and was heading for the kitchen when she realized she wasn't alone in the flat; someone was sitting in Sherlock's chair. She froze, then gave a small laugh when she recognized her husband's profile even in the dimness of the sitting room. "Why haven't you put any lights on, Sherlock?" she asked, reaching for the control pad on the wall.

"No, don't," he said, his voice rumbling from the darkness and sending a delightful shiver up her spine. She loved it when he did that, deepened the timbre of his voice. It meant danger to enemies but something very, very different to her. "Come sit with, Molly."

She toed off her shoes and did as he asked, climbing into his lap and settling her head against his shoulder. "I thought you and John were headed off planet for a couple of weeks, that's what your message said. Changed your mind? Case solved already?" Then she did a bit of a double take, reaching up to run her fingers through his hair, sleeked back from his forehead and straightened. "Let me guess, you had to do a bit of a disguise?"

"Do you like it?" His eyes glittered oddly in the ambient light, and Molly tilted her head, considering, as she continued to rake her fingers gently through the cropped locks.

"I do, actually," she finally decided. "I'll have to see it in better light before you leave, of course – you are still leaving, aren't you?"

"Yes, I am leaving. Before the end of the night." He sounded odd, but before Molly could ask him if anything was wrong, Sherlock pulled her into his embrace, leaning his head down to capture a demanding kiss. She returned it willingly, happy to have her husband to herself for even a little bit before he dashed off to the Magnussen Colony in pursuit of the suspect he and John had been chasing down for the past few days. She'd resigned herself to not seeing him for at least two weeks, so this was a lovely surprise.

She squeaked as he broke the kiss and rose suddenly to his feet, easily carrying her slight weight, his hands moving down to cradle her bum as he walked them to their bedroom. She twined her arms around his neck and giggled, peppering his face and throat with kisses, unable to resist running her fingers through his sleek black hair as she did so. "Feels different," she murmured into his neck as they reached the bedroom door. He pushed it all the way open with his hip, not bothering with an answer to her comment.

Not that she needed one, of course; he already knew it felt different, but at least after five years of marriage he'd finally learned not to tell her when she was pointing out the obvious.

He'd also learned how to surprise her at every turn; instead of lowering her to the bed and removing his own clothes while she stripped for his appreciative gaze, he settled her back on his lap as he sat down. Of course, since he was only wearing one of his dressing gowns – the silky blue one from the feel of it, although color was difficult to make out at the moment – there wasn't much stripping for him to do. But when she reached for the ties, he tugged her hands away, twisting them deftly behind her back as he brought his lips to hers for another hungry kiss.

His tongue insinuated itself between her lips as he held her so tightly against his body, his erection pressing with the same eagerness, or so she fancied, between her legs. She sighed and opened for him with both mouth and legs, allowing him this unusual show of aggressive dominance and rather enjoying it, truth be told. "Tell me to fuck you," he growled in her ear as he finally released her mouth.

"Oh, God, yes, please," she sighed in response, but he released one hand from her wrists to grab her chin, holding it firmly but not painfully as he peered into her eyes.

"Tell me to fuck you," he commanded, and that odd intensity was back in his eyes. She could see a little better now that her eyes had adjusted to the dimness, and wondered if her own pupils were blown as far back as his. "Tell me," he repeated, as if he needed to hear those very words for some reason.

Excited and almost painfully aroused, Molly obediently replied, "Fuck me, Sherlock."

He let out his breath in a loud exhalation, reaching down between them to stroke his fingers along the seam of her trousers, already damp from her arousal. "For tonight, I demand a title," he said, an arrogance to his voice she rarely heard directed toward her. "Call me Khan, Molly. Can you do that for me?"

She nodded, nearly stumbling over the words as she replied, "Oh, yes, God yes. Khan. Fuck me, Khan!" She was bolder now, so excited by the role play Sherlock was dictating that her nipples ached. She squirmed in his hold, trying to get more friction between her legs, but he suddenly flipped them so that she was lying flat on the bed with his body over hers.

"Say it again," he demanded, his voice ragged, his fingers working feverishly to divest her of her clothing.

"Khan," she moaned as he freed her breasts and lowered his mouth to capture a nipple between his teeth. Now that her hands were free, they moved automatically to his head, seeking purchase on his temporarily altered hair, the strands shorter and far straighter than she was used to but still soft to the touch. "Oh, please, Khan, please…" Her voice fell off into incoherent moans as he moved down her body, nipping and sucking at her flesh before settling between her legs.

Sherlock had always been enthusiastic about this particular activity, but tonight he was like a man possessed, as if the need to make her come was his sole motivation in life. All in all, Molly approved; even if this interlude was partially to help him to settle into whatever his temporary persona was going to be using while on the case, she was certainly reaping the benefits! Her moans soon became breathy gasps, and then sharp little cries as she felt herself hurtling toward the edge, driven along by Sherlock's fingers suddenly diving into her cunt while his tongue worked her clit with a savagery she'd never imagined him capable of.

Oh yes, she thought as she cried out her release, fingers tightening their grasp on his hair; whatever was driving Sherlock tonight, she definitely approved.

She approved even more when he surged up her body, kissing her senseless as he positioned himself and drove deep within her, while the aftershocks were still trembling through her body. She clutched his shoulders and tilted her hips, crossing her legs behind his back at the ankles in order to secure herself for what was certain to be along, satisfying bout of mattress wrestling.

She wasn't disappointed; Sherlock continued to act like a man driven by demons of the most intensely lustful sort, Molly thought deliriously as he reached down and slid his finger against her clit. She didn't always mange a second climax during sex, especially not after he'd worked her with his mouth, but the aura of danger, the edge of excitement and desperation, all served to bring her easily to another heady dive over the cliff of ecstasy.

Not long after Molly's second orgasm, a roar ripped itself from Sherlock's throat, and she felt him coming, filling her beautifully as he tensed and flexed above her. She ran soothing hands down his back, lowering her legs as the sweet tension they'd both enjoyed drained from them, leaving her feeling drowsy and lethargic for a change. Usually she would cuddle for a bit and then get up to grab something to eat, but not this evening. Instead she wormed her way out from beneath Sherlock's body and under the covers, holding them up and waiting as he joined her, wrapping his sweat-streaked body around hers, pressing soft kisses to her shoulder as she twined their fingers together.

She fell asleep that way, sated and happy, but awoke sometime during the dark of the night alone. The case, of course; he'd said it was just a brief stopover, but she couldn't help the surge of disappointment that came over her when she listened to his recorded voice telling her he'd wanted to let her sleep. She considered getting up and fixing herself something to eat, then groaned and rolled over, wrapping herself in the warmth of the duvet, her eyes fluttering shut, her last waking thoughts full of love for her husband, and hopes that he would stay safe while off-planet.

oOo

It was done. Khan watched the sleeping woman still snuggled beneath the covers of the bed he'd just abandoned. He'd redonned his clothing and had been about to leave when something drew him back to the bedroom. He stood in the doorway, his emotions conflicted, a disconcerting sensation for him. He'd always been the master of his emotions; he'd always felt the certainty of knowing his actions to be the right ones, the justified ones, but now he felt a twinge of something not unlike guilt at the sight of Molly Hooper-Holmes sleeping so peacefully after their ferocious lovemaking. He had lied to her, yes; some would call what had just happened between them rape, since she had no idea that the man she'd had sex with wasn't her husband. But he'd given her the closest thing to the truth that he could when he demanded that she call him by his true name.

Eventually, when the truth did come out, she would at least have the satisfaction of knowing that he'd done that much for her. And when she discovered that she was finally going to be able to have the child she'd longed for…he only hoped that would go a long way toward helping her to forgive him.

"Goodbye, Molly," he whispered, then turned and left her behind. She was now part of his past, and he had a great deal to try and accomplish in the near future. He needed to focus, not linger in her presence or relive memories he had no right to cherish.

But cherish them he would; he was Khan Noonian Singh, literally born to be a leader, to do what was necessary without fretting over consequences or second guessing himself, and he wasn't about to start now, just because one small human woman had affected him more strongly than he'd expected her to.

oOo

As soon as Sherlock entered the flat, he knew something had happened. Molly was sitting curled up on the faux-leather sofa, her knees to her chest, staring at him wide-eyed. He started to go to her but stopped as she flinched. "What's wrong, what's happened?" he asked softly, eyes darting over her form, attempting to deduce what terrible thing had happened to his wife while he'd been off-planet chasing after a phantom.

He'd been gone for over a month, rather than the two weeks the case should have taken, and all because someone – not the suspect, he'd been captured only four days ago and was certainly no criminal mastermind – had very carefully made sure that Sherlock and John stayed two steps behind their target, a blackmailer turned murderer.

It was a mystery, and one that needed solving urgently – he had no desire to match wits with yet another Moriarty-imitator – but not so urgently as the matter of what had upset Molly. He knew she hated when he deduced her, but if she didn't answer him soon then he would be forced to…

"I'm pregnant."

Sherlock's mind went completely blank as he attempted to process those two quiet words. The doctors they'd seen had been quite definite in their diagnosis; Molly had a genetic defect in her reproductive system that could only be corrected by extensive gene therapy. Which was prohibited by law. There was only one way she could have conceived a child, a way that should have been utterly impossible; his own research had proven that.

He slowly, carefully moved to sit in his chair, making sure to face her the entire time as he did so, to maintain eye contact. Her body language told him in no uncertain terms that she was terrified, but it was more than that; there was an element of self-loathing to her expression and the way she huddled into herself that he'd seen on victims of assault. The idea of someone forcing themselves on his wife filled him with a towering rage while at the same time twisting his gut with nausea, but he tamped down on both reactions, reminding himself that the body was merely transport, the mind was all, until he'd calmed enough to speak. "Tell me what happened."

And she did, the words spilling out of her in a torrent. About the night he'd supposedly returned to the flat before leaving for the case, even though he knew – as did she, now – that he'd already left by the time this mysterious imposter had entered their lives. She only broke down when she described how the man had told her to call him 'Khan', and Sherlock was by her side in an instant, pulling her into his embrace as she sobbed out a series of entirely unnecessary apologies and self-recriminations.

When the emotional storm was finally spent, he continued to hold her, knowing it was what she needed. He might have come late to an understanding that love wasn't a chemical defect found on the losing side, but he understood it quite well now, and Molly had been the one to teach it to him. So he soothed her as best he could, whispering his love to her but not forgiveness, because she'd done nothing that required forgiving, as he told her over and over.

When she was ready to speak again, she told him quite calmly that she had no intentions of terminating the pregnancy. He was shocked that she'd even considered the idea at all, and wasted no time in letting her know that. "Molly, we've wanted a child for years now, there's no way we can let this opportunity pass us by, no matter how it came about." His expression darkened. "Even if my suspicions as to the identity of this imposter turn out to be correct."

"You think he's an Augment," Molly said quietly as she gazed up at him, her head resting on his shoulder.

Sherlock nodded grimly. "That's the only way you could have conceived without genetic intervention. I researched your condition quite thoroughly once you were diagnosed," he added. "But since all the Augments were killed three hundred years ago, the possibility of in vitro fertilization from a donor seemed impossible."

Molly sighed and nestled even closer to him, his arms encircling her protectively as she said, "But like you always say, Sherlock; once you've eliminated the impossible, whatever remains, however improbable…"

"Must be the truth," he finished softly when her voice trailed off into silence. The two of them contemplated the impossible possibility that had invaded their lives, and although Sherlock would still have happily murdered the unknown lookalike if he were standing before them now, he could not deny feeling a certain amount of gratitude toward him as well, for giving Molly the child she'd wanted so desperately.

"He didn't hurt me," Molly said quietly, eyes trained on the middle distance as she spoke. "He didn't force me except in the sense that he was pretending to be you. But I think…I think this is why he did it. I don't have anything to back that up; I can't say I can look back and deduce anything, but Sherlock…why else would he do it? Except to give me – us – a baby?"

He shook his head wordlessly and laid his cheek on the top of her head.

They remained that way for over an hour, until the changes in Molly's breathing told Sherlock she'd drifted off into sleep. He eased her onto the sofa until she was lying down, then removed his coat and laid it gently over her before heading for the computer and grimly diving into the first of many frustrating hours of research.

If he'd known how the answer would come to them, he wouldn't have bothered with that futile search. Four months later he and Molly were sitting together on the sofa when the news alert came over the computer, detailing the horrifying explosion at the Kelvan Memorial Archive less than five kilometers from St. Bart's Hospital. And when the face of the perpetrator was shown, the rogue Starfleet officer Commander John Harrison, they had the answer to the ongoing mystery of just who had fathered the baby currently swelling Molly's midsection in a gentle curve.

Two months after that, when the news broke that John Harrison was actually the Augment leader Khan Noonian Singh, with all the accompanying scandal surrounding Admiral Marcus and the shadowy organization known as Section 31, they had the final piece of the puzzle.

"It doesn't matter," Molly said firmly when Sherlock announced his intentions of having his best computer man, Billy Wiggins, dig up the details that Starfleet still hadn't released to the public. "Whether he's dead or in prison, it doesn't matter, Sherlock," she insisted, pulling him down for a lingering kiss. "What he did to me, to us, was wrong, but he gave us a precious, irreplaceable gift and I won't waste a single moment fretting over the past." She laid Sherlock's hand on the swell of her abdomen, and he smiled.

Two months later their son was born, Robert John Holmes. And if his middle name was in honor of two very different men, that was their secret to keep.