"So. You're back again, Merlin?" Merlin glanced toward the Doctor and smiled.

"As are you, old friend."

The Doctor smiled slightly, "I am. I've been here for a while this time actually, got a proper job and everything. They even gave me an office."

Merlin grinned and relaxed back into his 'Professor' chair.

"How very official sounding. Should I bother asking how much time you spend in it?"

Taking the sofa the Doctor hummed, "Weeell, not much, but a little, more since a young lady started asking for proper lessons. I always forget how excitable young humans are and… distractible. That's before you consider their tendency to wander off after anything that seems likely to mate with them given half a chance."

Merlin groaned, "Again Doctor? And here I thought that the grey hair was a sign of you growing up and leaving the 'excitable' types be. Plus, they stick to humans, not 'things'"

"Never growing up Merlin, it's a terrible idea. Believe me though, I am definitely not her type, she'd be more appreciative of my- of Clara, and You of all people can't comment on the humans-only trend. Or deviating."

"Hey, that's unfair, I am careful. Usually."

"Uhuh. Lady of the Lake."

"You know she's off limits."

The Doctor did know and tilted his head, but he was one of the few who also knew Merlin.

"The Faye Princess." Merlin cleared his throat.

"We were more um… friends with benefits than a thing. She wasn't willing to take the leannan sìth back without some kind of compromise."

"Still counts, Merlin. Jack."

"Oh come on, he was human."

"Indeed. WAS, past-tense, and don't think I didn't hear about what you pair did to poor Shakespeare that one time. The Dryad, Mr I-was-frozen-in-a-tree."

"Oh fuck, well the bard wasn't exactly complaining about it. The legend does become somewhat less family rated if it features a Warlock being invited to a magic party by a pretty girl, then rather foolishly following a beautiful, friendly Dryad girl 'home' while rat-arsed and getting slightly...carried away...without realising time passes differently in that realm. It really didn't seem that long. I couldn't exactly tell them I drank too much at a Beltane fire and was away for long enough with a girl that they thought I was trapped forever." He rolled his eyes.

"Tell you what though, it was a whole new meaning of 'I'm never drinking again.'"

"Uhuh. Family friendly is it now?" The Doctor looked as though he doubted Merlin's capacity there.

Merlin allowed himself to properly laugh then, "Oh, shut up! She had descendents you know, you even met one of them. It's not like they want to hear about great-granny's prowess in seduction. It's good to see you again Doctor."

"And you Merlin, and you. The offer still stands by the way. As always."

Merlin was absentmindedly playing with the light, bending it into elaborate displays, "And the answer is always the same, isn't it. You could have chosen anywhere to get a 'proper job' as you called it, to guard or study whatever you are really here for, but you didn't, you chose to be a university Professor, surrounded by those still unembittered. Wide eyed and fascinated by the world, I understand why too. I can't offer you that and we both know it, I'm an old man Doctor, jaded, no matter how I look, just like your last face. I needed to see the same thing as you did. I can't allow myself to withdraw again, and neither can you. I love spending time with you and Jack. It helps me hold onto sanity, but travelling together would destroy us all- and goddess knows what else. We all need to be reminded of the forgiveness of youth, in between times." He smiled gently at his old friend, despite denying him. They'd seen each other at low points as well as high and accepted each other for all of it.

Merlin cleared his throat and waved a hand, "I like the new face you know, it suits you. Definitely one of my favourites. I bet you still have a voice they don't listen to though." He paused and looked around his own office. "When do I get to meet your new pupil then? Or do I have to go to class and guess?"

The Doctor closed his eyes and smirked, "Well where's the fun if I just tell you?"

Merlin snorted "Sometimes you're worse than Kilgarrah."

"I'll take that as a compliment. I rather like him, when he isn't trying to roast people. How is your

dragon?"

"Sleeping. Thought he'd stretch his wings a bit and is curled up somewhere near Iceland, they have some lovely volcanoes up there. Apparently it feels 'homey.'"

The Doctor's bushy eyebrow could rival Gaius' own. "Can't say I've ever felt particularly at home in volcanoes. Just make sure you check out the dust up there. Volcanic dust can be dangerous." The Doctor frowned and Merlin knew he was lost in a memory. He waited patiently for it to pass.

"I will. Where were you?"
"Pompeii. Mount Vesuvius. It was a fixed point." Merlin allowed his empathy to flow around the Doctor's mind.

"I met her once you know. Donna Noble. Well, twice. You took her back for a picnic once, a long time ago and she saw me. Said I was far too skinny and made me eat a banana. I'd never seen one before and she had to show me how. She felt different, but I was too young to understand then. Later, much, much later, I met her looking for you. I almost called you then but it wasn't time yet."

The Doctor registered surprise but reminded himself that here was one of the precious few who understood, who knew to some extent the burden of knowing, and of allowing things to unfold that must not be altered. "I didn't meet you until you were younger."

Merlin smiled wryly, "You wouldn't let me travel with you when you heard my name, and started cursing archaeologists."

"They're always interfering."

"They make you laugh."

"That's not a compliment." The Doctor's eyebrows did something complicated.

"She thought it was." They were quiet for a minute.

"Sorry. I know you miss her, I shouldn't have slipped."

The Doctor inclined his head, accepting the apology. He wasn't the only time traveller to have visited Merlin after all.

"So what are you teaching this lifetime?" The gruffness of his voice was only a little more evident than usual so Merlin relaxed and summoned himself a cup of tea.

"History of Medicine. I was feeling nostalgic. It did a brilliant job of reminding me how much I do not miss cleaning leech tanks and the lack of effective anaesthetics. Gaius had plenty of faults, but in many ways he was a man ahead of his time, though I must have cost him a fortune in broken beakers."

The doctor snorted, "I don't believe for a minute that you didn't fix those with illegal fusion."

Merlin glared, "Magic. And maybe a little, but not all. He was ever so cross when I accidentally turned one into crystal that one time, watched me like a hawk for the next month. Even the Prince noticed." He snorted.

"Can I get you anything?" Merlin gestured to the tea.

"Ah, I'm not much of a tea drinker this time 'round." Merlin shrugged and didn't probe that.

"Well, is your new 'student' taking exams this semester or a more practical test of understanding?

The Doctor's lips quirked upwards a little, "Oh, we might have to take a field trip of sorts, she does have a better imagination than some of my friends, which is refreshing and jarring in equal measure. Perception filters don't work on her either."
"I didn't think anything could shock you anymore Doctor." Merlin suppressed a chuckle at the disgruntled look the man displayed.

"Ah. Speaking of shocks, and fieldtrips. I don't suppose you'd be willing to babysit an old friend of mine for the duration of our brief excursion?"

Merlin looked at the Doctor with open suspicion. "What kind of old friend needs a guard at all times then?" He added the Warlock Eyebrow for effect.

"Ah, yes. The kind who you have long and complicated histories with and alternately try desperately to save and kill, with compromised mental stability. Maybe a little bit more… challenging, than would suit the average Human."

Merlin glared, "Doctor. What are you Not telling me."

"I made a deal of sorts, the tricky kind."

"DOCTOR!"
"So in return for not killing Missy, I ensure she doesn't indulge her megalomania and try to conquer the universe. We were friends once. Good friends. Then he became fractured and lost. He was betrayed and they turned his mind against him. Now there's just me and her left, and I can't kill Missy, and Missy can't bring herself to kill me."

Merlin sighed, rolling his eyes. "Shit, I hate those choices. So is she going to take over the universe?"

The Doctor smirked, "Only if we let her."Merlin shook his head at the old man and huffed. "Is she at least interesting?"

The Doctor groaned. "She's psychotic, smirks, has a lust for power, dark haired and flirts as she breathes. Half the time she speaks in riddles, most of the rest she's trying to wind people up and provoke a reaction, preferably a violent or passionate one. Skilled in telepathy. She's exactly your type. Don't touch. Don't even look." He glared at the ancient warlock, and even raised a warning finger.

He smirked back, "Are you sure you want to go gallivanting after all?"

"Only if you are willing to take a watch."

Merlin stretched and looked the Doctor over critically, concluding that he'd been doing this for quite some time, not sleeping by the smudges under his eyes, in need of a distraction, any distraction.

"I'll do it. No promises about ignoring her. I've been trapped and guarded as a monster enough to have baggage about it. No touching, no thinking."

"And don't listen to her."

"Why not Doctor?"

He cocked a bushy brow, "Because you listening to brilliant, beautiful women never ends well. This one can escape crystal caves in her sleep, so don't. I've been here 100 years already, and have another 900 to go."

Merlin chuckled. "Fine. No listening. You go with the youngster, and I'll Timelady sit every century or so, yeah? I will even solemnly swear not to reveal her existence to Jack."

He smirked at the look of horror that crossed the Doctor's face. "No. Oh no, no, no, no. He can never know. The two must never meet!"

"Does he know that you are on an extended visit?"

The doctor rolled his eyes, "Of course Harkness knows."

Merlin ignored the attitude, "Did you tell him you idiot?"

Guilt flared in his eyes, giving him away as clearly as shouting would have.
"Right, one last condition, you go and tell the Captain about this self imposed guard duty, how long it will be, and you grovel for not telling him already. I can wait as long it takes Doctor, I've got time, and two hundred essays to mark."

"Uhuh. And are there any other demands you'd like to make while we're at it? Maybe some Altarian vodka, the co-ordinates for the other homeworld of dragons perhaps, or a tracking beacon?"

Merlin snorted, "Yes, but I won't. Never give anyone that drink again, it's an act of hate, you will take me to that world anyway one day, and I hardly need a beacon to track anyone. Just try to remember the name Ianto, he's Jack's Rose." He frowned, "It's going to matter soon."

Pressing his lips together and running a hand through his hair the Doctor nodded, "Right. Something you've Seen, or just observed?"

Merlin shook his head, his voice gentle, "You know I can't tell you that, old friend."

He had yet to tell the Doctor he'd been accidentally slipping through time again, though he suspected that was important, the man had enough on his mind, it could wait until the man had gone off world for a bit. This incarnation seemed less prone to distraction and the TARDIS had decided to be more co-operative since River Song had spoken to her, so he very rarely missed his intended destination or was late now.

The Doctor hummed and watched his friend carefully, he'd find out what the problem was when he got back. Prodding Merlin for information when he'd no intention of giving it yet was an exercise in frustration for all parties. He knew that well enough by now. Maybe he should enlist Jack's help, though Jack's standard method of helping was more Gwaine-like than anything else, so possibly not ideal. Still, he'd been human once, so often understood the warlock a little better than the Timelord did.

"Fine. I'll do it. Just don't start doing that thing with your face, like you think you've won something, it looks wrong."

"Too late Doctor, it's already doing the thing."

The Doctor scowled, "That face is why you ended up being remembered as an old wizened man with a beard that trails in puddles."

"No it isn't. All warlocks and witches look smug or smirk, at least 40% of the time. It's in our

code."
"Your code? What code, you have no code! You've barely got suggested guidelines you lot."

"Oi! I could have a code, I just haven't got around to writing one yet, and if there was one, smirking would be in it. Smirking, and smelling of strange herbs, and mad hair, and… and long fingers! Or something. It's not like you have one either, some secret Timelord code."

The Doctor folded his arms, "No, but we take an oath, and have Rules. Lots of Rules."

Merlin snorted, "Which you ignore."

"I do not."

"Do too."

"Stop being childish!"

"Stop denying it then."

The Doctor sighed, scowling. "Ok, I suppose sometimes, just in specific circumstances I might be a little prone to some casual rule breaking. Only the silly ones though." Merlin narrowed his eyes, "Recently. Nothing major in the the important Rules broken recently."

Merlin nodded, "Well then. If you promise not to break the universe with Miss imagination later I'll see you tomorrow and Missy sit. Is it just 'Missy' or does she demand 'My Lady' as well?"

The doctor rolled his eyes, "Don't even suggest it, though technically she is a Time Lady. They were more thoroughly starched than any of the humans who expect the title."

"Hmm. All of the starched ones were evil. Or furious. The corsets seemed to be intended to hold the anger in, it backfired horribly as a plan. Terribly uncomfortable things though, I can understand why they were vengeful. As bad as chainmail to move in."

The Doctor arched a bushy eyebrow, "You know this from experience?"

"I lost a bet, ok? And I got bored for a bit of the Elizabethan era. They all seemed to lapse back into the whole witch-hunting mentality, but added catholics to the list, and it was easier with more than one disguise. I owe Leon five silver pieces."

The Doctor's scowl had deepened at the casual mention of witch-hunts. "Ugh, why are humans such idiots."

Merlin looked pointedly at the Doctor, "Because, my dear Doctor, they live, and most are barely more than children. You on the other hand are a Gallifreyan Timelord, have lived so long you've lost track, seen wonders, and yet have sat with Emrys drinking tea, and Altarian vodka telling me that magic is not real. Bit cheeky to call the humans idiots until you can admit I am what I say I am, after you have seen it being used."

"It's not magic, it's..."

Merlin rolled his eyes. "All science. Yes, you've said that already. Then stop calling them idiots for fearing what they can't explain." The Doctor huffed but didn't argue.

"If you ever want to properly destroy those witches you picked up from Shakespeare you know where I am."

"They are not witches they're.."

"Carrionites" Merlin finished with him. "I know. But on my planet they use my forces, and they really screwed the flow up back then, took me years to properly untangle the mess they made of it. I'm still pretty pissed at them you know, and I felt their magical signature, I'm stronger."

The Doctor eyed him "No."

"No? I thought you had a friend who wants the universe, why are you keeping possible resources in the next room?"

"Next room! My TARDIS is a whole world behind one door. One room." He scoffed, "You kept a sidhe staff under your bed with a mortal enemy upstairs who kept trying to have you killed."

"Yes, and it was a terrible idea, from a 17 year old."
"The carrionites aren't under my bed."

"Well that's good, but you haven't been using it anyway so goodness knows what's under there by now." Merlin grimaced in distaste. He had always made a habit of avoiding 'under the bed', nothing good was ever there. Bodies, slugs, royal socks, mouldy apple cores and shadow creatures, yes, but nothing good. He certainly wasn't about to volunteer to check this one.

"I'll think about it." The Doctor's lips curled upwards at the look of shock from Merlin, he clearly hadn't expected to win what was more bickering than an argument.

"Thank you Doctor." He spoke quietly, and ran a hand through his once again unruly hair,

"I have to give a lecture on the historical use of honey in medicine tomorrow morning, but I will be at yours in the afternoon, see if I can't spot your new friend, then we can go and see your old friend."
A comfortable silence descended over them then. When the Doctor dragged himself upright again and strode purposefully towards the door Merlin smiled, "Not that you believe in it but good luck. He'll forgive you Doctor, he always does."

His eyes sad the Timelord glanced back, "He shouldn't. I always end up hurting them."

Merlin nodded, "Perhaps, but he will do it anyway, because you taught him how, and because we all need that in the end. First time he's met this face, isn't it. I look forward to hearing his response. Later. Take care of yourself Doctor."

"Don't I always?"

Merlin eyebrow crept upwards, "That you can say that in your 13th incarnation with a straight face concerns me more than it ought."

"Fine. I will. Can't have you missing a lecture and not learning anything, can we?" and the space he had been in was suddenly empty. Merlin just shook his head and sipped at the tea he never allowed to cool.

He did after all have essays to mark, and research on this friend-nemesis of the Doctor to do.