A/N: If John seems OOC in this - GOOD! He's meant to. All is explained. If the Doctor seems OOC - BOO! I apologise and will work hard to rectify this in future. Yes, this is meant to be slightly subtly distressing. I hope that comes across. It's hard to tell because it's from the Doctor's POV and he tends not to always connect the dots, emotionally. Let me know what you think!
Disclaimer: All the characters belong to Moffat, Gratis, BBC et al

Symbiosis

1. John Watson had a very delightful response to grief.

Or so the Doctor asserted. Having met trillions of creatures spanning more galaxies than he could count, he had seen everything from stoic disregard to violent war, inner peace and acceptance to slow descent into madness. He'd seen denial and failed attempts at resurrection. He'd seen acts of distraction, exertion, stimulation, pleasure, pain. He'd seen them turn to Faith - or, conversely, turn bitterly from it. He'd seen them seek comfort in loved ones or recoil from all touch. He'd heard them talk feverishly of the deceased, fixated, desperate, as if the strength of memory could bring them back. And of course he'd heard deafening silence that choked the air just as, perhaps, those thoughts choked them.

And this - this was quite literally universal. How strange and wonderful, then, to find a planet that encompassed every one of these reactions.

And yet, while the inhabitants subconsciously knew there were myriad responses to the death of a loved one, there was a strange social stigma, an expectation for them to all react the same way.

Tears.

Or, no. No, not quite, he was getting ahead of himself again, for the tears came later. Because first there was supposed to be this period of the griever denying all possibility of the loved one's passing - seeking clues, roving over the situation in their heads, struggling to hone in on a loophole or mistake, something, anything, somewhere it'd all gone wrong - and in finding nothing they were meant to be angry: at whom, though, it was always hard to tell; angry at themselves for letting the loved one die, angry at the loved one for dying, angry at the reason the person died (be it person, illness, accident, etc), or even maybe just angry they couldn't let it go.

Sometimes this was when the tears came. After all, society dictated this was a reasonable point at which the tears could come. But the Doctor knew quite a lot of sentient beings who didn't cry; not crying seemed perfectly reasonable to him. But those around the aggrieved kept asking why and insisting upon "letting it all out" and the whole affair was quite troubling.

So onward and upward. This human theory continued that the aggrieved desperately (sometimes silently, other times with a shout that tore the voice from their throats) said they'd do anything to have this sorted: which for some people meant I'd give anything to have them back again, bring them back, but for other people was closer to They're never coming back but I can't stop wanting - just, please, make it stop hurting. I'll do anything if you make this feeling go away. But the feeling didn't and no one was listening and the bargain went unanswered, and then realisation set in - this was it, this was real, nothing would change what happened and oh god I must figure out who I am without them and the Doctor knew firsthand, 900+ years over, what a painstaking procedure that dissection and reconstruction of existential musculature could be.

If tears hadn't come by now, those around the aggrieved were deeply distressed.

The grief was healthy, humans were told. Don't hold it in. Talk about it. You'll get there, love.

Acceptance. The ultimate goal at the end of the road. There was no prize, no pot of gold, no Emerald City, no marathon high - merely the funny feeling that it didn't hurt as much as it once had and maybe, just maybe you ought to feel guilty for not obsessing the way you used to or for finding someone new and not thinking of them first, or the strange but pleasant sensation of remembering with a mix of happy and sad, smiling despite yourself and not fighting back tears.

Tears.

The predictable response for a human following the loss of one they loved.

But what if there were a way - ways, even - to side-step all that messiness and just come to terms with it all in one go? The Doctor pondered this as he watched the man in the cafe booth turn a page absentmindedly. Why did it always have to go a certain way? Why couldn't extraordinary people come up with extraordinary coping skills?

The Doctor had a theory.

A small one, yes, and difficult to prove, but it had taken root and was starting to grow and needed tending to and lots of water and sunshine - and maybe just a touch of arsenic.

It needed John Watson.

Just from brief observation John proved to be anything but predictable; the Doctor knew. He had not responded to loss in the socially expected, socially accepted fashion. John Watson wasn't crying, hadn't cried, wouldn't cry.

In lieu of crying, John Watson was pretending to read.

The Doctor easily slid into the booth seat opposite John. "Hello!" he said brightly when John looked up. Confusion with veiled suspicion.

Good. Suspicion was good. Suspicion kept him sharp.

"Alright?" John replied non-commitally. "What's this about?"

Blunt. Interesting. Obviously intelligent, or else Sherlock Holmes wouldn't have bothered with him, but perhaps lacking either the capability or the patience for subtlety. That said, the Doctor would be a fool to underestimate him - John was likely extremely straightforward in how he expressed his views, but several years of association with Sherlock probably had honed his abilities to pick up on evasion techniques and to acquire some of the detective's deftness for putting two and two together quite quickly. Oh, yes, very good indeed. The Doctor grinned. He could work with this.

"Just noticed your book," the Doctor said innocently. "Very good read. Entertaining. Even slightly convincing. Completely wrong, of course."

"Of course," John said with a sigh, almost as if talking to someone else. He caught himself and straightened up. "Who did you say you were again?"

"Didn't, I'm the Doctor." He smiled again and held out his hand.

Dubiously, John shook it. "Nice to meet you," he said. "John. Doctor of what, exactly?"

"Oh, all sorts, not important at the moment," the Doctor said dismissively. "What's really quite crucial at this moment is the fact you've been sitting in a cafe for nearly four hours since you got off your shift at the clinic - no, I've not been stalking you - reading a book on quantum physics when you've never even liked the subject and haven't touched the stuff since Uni - no, I haven't been at your personal records - you haven't ordered anything beyond a tea and yet they haven't thrown you out so this is obviously a place you frequent quite often, perhaps you see it as a safe haven - don't worry, I'm not about to psychoanalyse you - but the most interesting thing of all is you've been staring at that same page - based on the thumb creases, I'd say for about 30 minutes now - keeping up that farce of pretending to read, only you keep forgetting and staring off into space and no one has come to disturb you, friend or wait staff, so they must be quite used to your behaviour and habits and they have their roles in this game of yours and after several rebukes in the beginning they've learned not to break character."

John sat there, stunned. The Doctor could see the wheels in his head turning, a flicker of remembrance, the twinge of discomfort, and predictably the desire to flee - which was why the Doctor went in for the kill.

"So, tell me, John," he concluded, a blinding smile on his face, "Why are you avoiding your flat?"

John cleared his throat. When he spoke, his voice came out steady. "What are you?" he asked evenly.

What. Not who. Fascinating.

"I already told you, I'm - "

"The Doctor, yeah, got that the first time, thanks," John said softly, with an almost dangerous lilt that reminded the Doctor of someone else.

Yes.

Oh, this was lovely. Human innovation and the Doctor's own cleverness never ceased to amaze him.

"But there are lots of different types of doctors, aren't there," John went on, still with that almost hypnotic timbre. "Me? I have my MSSB and have practiced in a fair few settings round the world, but judging by your disturbingly accurate deduction skills I reckon you already knew that."

The Doctor stayed silent, waiting with bated breath.

A peculiar smile came over John's features and he laughed humourlessly and continued. "So tell us, Doctor. What are you? Don't think I missed that capital letter. You say it like it's your name, not your profession. Like you've either got nothing else to you and all you are is what's on the surface...or like you've got everything to you, and that's an awful lot needs hiding."

The Doctor waited. He restrained a feral grin at how well this whole thing was playing out.

He had never been more pleased with himself.

And he had never been more pleased with humanity. Just when he thought they couldn't surprise him any further, he saw something new and fell in love all over again. And right this very minute he was terribly infatuated with the concept that was John Watson - this beautiful, haunted, fractured example of what humans were capable of when faced with terrible pain. Healing through osmosis and redefinition! Resurrection through evolution! This specimen kept Sherlock alive by becoming him, but simultaneously did not lose himself completely. Brilliant! The perfect hybrid, the perfect duality, the perfect solution to an impossible conundrum. The Doctor wanted to study him for hours: John's reactions, his strategies, his mind - and his understated, morbid, socially unaccepted expression of love and loss.

Sherlock would be proud.

No. More than proud.

Sherlock would be intoxicated.

"Got several meanings, hasn't it?" John said innocently. "Doctor. Many incarnations, archaic permutations. Latin: docere, to teach. Now, lately, it conjures up an image of those blokes in white coats. But, as I'm sure someone of your obvious intelligence is already aware, it used to refer to religious fellows, Apostles and priests. Astronomers, professors. Scientists and philosophers with mastery of a subject or discipline others may only dream of puttering through, right? And even today's definition - I guess the closest synonym is 'healer,' but that's often inaccurate as well, because those men in white coats harm as many as they heal. Maybe it's because they don't know any better, or maybe because they do but it's all in the name of the greater good, so we try to tell ourselves that it's necessary and justified and that makes it okay. With time we start to believe it, until that one instance when we don't, and that moment - that moment is crippling, because it always strips the nerves to see yourself as you are, doesn't it? But we still get up the next morning and get dressed and brush our teeth and drive to work and do it all again."

He paused. "And your capital letter, Doctor, manages to encompass all those incarnations at once, doesn't it? How many have you taught, studied, absolved, mastered? How many have you hurt for the greater good?"

The Doctor swallowed, his two hearts hammering.

"Please. Tell me, Doctor," John said, voice a touch gentler, more human. "What are you trying to teach me?"

In that moment the Doctor was reminded that John Watson the Original was still in there - this hybrid creature still needed reassurance and human connection, no matter how sarcastic and caustic it became.

"Your flat," he said, ignoring the question. "Why have you been avoiding it?"

"I don't know you," John said with a peculiar tone of firm dismissal.

"Then you have even less to lose by telling me," was the Doctor's reasonable reply.

"Not if you're connected to a crowd I find unpleasant," John retorted.

"Mycroft didn't send me," the Doctor said bluntly.

Blunt is good. John likes blunt.

John softened a bit, but his eyes were wary at the mention of Sherlock's brother's name. "Well, regardless. You clearly know things you shouldn't."

"Couldn't it just be I'm a genius?" The Doctor gave a winning smile.

John grimaced. "I tend not to play well with those."

"The flat, John," the Doctor said urgently. "This is important."

John snapped. "What is it with you and the bloody flat?" he hissed. "Obviously I don't want to go back because of what's just happened!"

"No." The Doctor narrowed his eyes. "That's not it. That's part of it, but that's not all. You suspect something, an idea is forming in that brilliant, hybrid mind of yours and you're terrified of the implications, terrified of what it might mean. So instead of allowing yourself to fully deduce - which would inevitably lead to pondering then wondering then predicting then obsessing then believing then waiting then wanting - and if you're wrong it could hurt so much more than anything has before in your life - you go to work all day then come back to this bloody cafe where no one talks to you and the tea is so terrible you let it go cold."

He took a sip of John's cold tea. God, it really was terrible.

"Was I right?" he asked when John still hadn't said anything.

John had a deeply annoyed look on his face. "We've got...an infestation," he said finally, rolling his eyes.

Ah. So he could be subtle. Well, subtle enough for the average human at any rate. It was more than the Doctor had expected. This was so delightful!

He nodded eagerly. "Yes?"

"I'm not a threat to anyone and today's feed of information is quantum fast, so anyone who wants to know anything already knows everything," John went on carelessly, but his eyes betrayed his confusion and hurt. "I'm reasonably sure Big Brother doesn't put much stock in my presence, so..."

"...why is he still watching the flat?" the Doctor concluded with a grim but triumphant smile.

"Yeah, exactly. So I keep thinking of all the reasons he wouldn't have ended the surveillance, except none of them make a lick of sense given the evidence."

"Except one," the Doctor said quietly.

John clenches his jaw. "Right," he says tightly. "Except one."

"Would that one be so horrible?" the Doctor asked, aiming for comforting but coming across curious.

John didn't seem to notice nor care he wasn't good with platitudes. Ah, right, the Doctor remembered. He was a hybrid now.

"Only if I'm wrong," John replied.

"Have you been wrong very often?"

John paused to think. "I've been right when it counts," he said finally.

"This counts," the Doctor reminded him gently. "Go home, John. There's a fireplace and better books and decent tea. And be sure to get some sleep - you'll be doing a lot of research tomorrow."

John smirked and didn't even ask how the Doctor knows what was in his flat. Either he had already come to a conclusion or he didn't care to think of one; the Doctor stared at him, fascinated. What a peculiar and lovely and terrifying thing it must be, to absorb the purest essence of a loved one into your Self so they kept growing and changing and evolving with you, so you might keep them always, protect them and yourself, forever.

Symbiosis, the Doctor decided, was new and heartbreaking. But he would be lying if he said he didn't find the whole affair tragically fascinating.

John smiled at him. "I expect so. Thank you, Doctor. I'm sorry if what I said offended you."

The Doctor shook his head. "No you're not, and I know you meant every word and would say it again in a heartbeat. Strange custom, that, apologising when one isn't sorry."

"Social grace," John said helpfully. "You seem to be a touch lacking. I could give you some lessons - "

"No no," the Doctor said hurriedly. "Thanks, though. Best be off. Lovely chat." And with that the Doctor dashed off to his TARDIS - but not before watching John pay the bill, gather his books and head home.

Closing the door, the Doctor smiled.

He wondered, though. When the dark-haired detective finally returned - and it was only a matter of time now, the Doctor knew - how would John react to having two Sherlocks in his head?

Oh yes. Humanity never ceased to amaze him.