A few hours on, and with my back to the tiled Pandorica on the wall I've been able to relax a bit. Well, I've stopped pacing. Well, it's not the frantic pace it was before. It's a nice, easy-going sort of pacing, that you wouldn't notice, unless you were locked in a cell with me and had nothing else to do by watch. "Sit down," Clara growls through her teeth. Clara is starting to get a little bored with captivity. Clara is starting to get a little tetchy.

I know a little bit about tetchy women. Not a lot, admittedly, but I know the key facts. For instance, if it's not a danger or an imposition, it is usually prudent to do what a tetchy woman is asking of you. I sit down.

"See the universe, you said…"

"Clara…"

"All of space and time, you said-"

"Clara, please."

"It'll be fun, you said."

That's a step too far. 'Boring' is an insult I just will not bear. "Tell me it's not. Look me in the eye and tell me it's not."

"I can't."

"See? See! You just like complaining, that's your problem-"

"No, I mean you haven't looked up from the floor. That mosaic over there, outside the cell, what's so special about it? Or scary. Scary might be a better word than special."

She might as well ask me what's so scary about alternate universes, or collapsing timelines, or the cruelty of madmen. Or libraries, if you must take things to their logical conclusion. It's not a story I can tell her. Don't get me wrong, I ought to. Telling her would equip her with the necessary knowledge and information to avoid, at all costs, falling into such circumstances herself. I should tell her all the stories. I should write down all the stories in a book and make a trillion copies and send them to every edge of the cosmos, to every planet in every galaxy.

'Don't Run Off: A Collection of Cautionary Tales, by The Doctor'

It's got a ring to it, actually.

I ought to. Does it count for anything if I'm just aware that I ought to? Anyway, I don't get a chance. No, that's a lie – I have more than enough time to start, but I would never have gotten to finish the tale, so it's a good thing I didn't. Clara will just have to wait for the book like everybody else, because there are footsteps in the corridor. Someone is coming. Specifically, three people, which is one more than left us, which is promising.

"Hello?" I call through the bars, before anybody comes into sight. "It's only me. I'm the big handsome misunderstanding in the cell with the attractive little misunderstanding."

Clara folds her arms, muttering, "You can't distract me with flattery." How does she always know my clever schemes? The woman's a mastermind…

Our captors return, Legionary and Legionaryette. They come first, ahead of new feet. The armour on this new arrival is of a better quality, and with more decorative flourish. There's a heavy red cloak swinging from his shoulders. He carries a short sword, rather than their spears, and his shield is of a heavier, brighter stuff, tacked all over with brass studs. And my conclusions, from all of this, from the way he holds himself, the pride and determination in his eye? The boss.

He comes right up to us. Looks at me dead on. Grimly silent. I feel Clara quail, but then again, there's steel bars between him and us.

I stick my hand out through them to be shaken. "Hello. How do you do?" Good manners are the cornerstone of good diplomacy. I did my thesis on that at the Academy. They laughed at me until they read it. Then they stopped laughing and gave me exasperated looks, but that's beside the point; whether they believed me or not I've found it to be very, very effective. A smile doesn't cost a thing, you know. Never fully dressed without one. Laugh and the world laughs with you.

I shouldn't have time to think all this. He's still just staring at me. But I keep the smile up. That's what's important here, is the smile, my stars, I wish he'd do something…

Eventually, something changes. He doesn't shake my hand, but there's a flare of something sharp and sentimental, and he barks over his shoulder, "Horace, bring those keys."

Horace, it would seem, is the name of the legionary. Which is good to know. Now I can drop the unintentionally diminutive '-ette' from the lady's epithet, even if I don't get her name. She can just be 'the legionary' now, no need for gender divisions. (This probably counts as cheating, but I can't imagine any of my current audience surviving so long as for it to matter, but you humans do away with the gender binary for a couple of hundred years. Don't worry about when. It's too far in your future to matter. Just trust me when I tell you it was very good fun, if a little difficult to govern, and I very much miss it when it gets reinstated. It was confusing, though. I could never have used the term 'legionaryette' during those couple of hundred years, I'd have been exiled. Sorry, I digress. I was being captured and diplomatic and I've digressed and spoiled the whole thing now. Sorry. I'll close these brackets now. Sorry.)

Horace, who before my digression was to bring the keys, brings the keys. He releases myself and Clara. Looks a bit confused about why, but good soldiers with good superiors don't question them. His obedience is a good sign. So is the fact that the lady is still holding out her spear, ready to herd us right back in there if we make one false move against her commander.

For the centurion's part, his steely face doesn't move, doesn't so much as twitch. There is, however, the very edge of a smile on his voice when he tells her, "Put it away, Flavia. Not necessary." (Horace and Flavia, by the way, just so you're all caught up. This isn't a digression, this is me making sure everybody's on the same metaphorical page as well as physical.) "This man" her leader tells her, "is exactly who he says he is."

Horace panics. Out of the side of his armour, he scrabbles for the sonic, and holds it out to me at arm's length as if I might bite. I accept it gently, graciously. Then, finally the Centurion's smile surfaces. He gives me the same closed-hand salute his subordinates gave the mural before. They follow his lead and give it to me now, and this time go down on one knee with it.

"Oh, no," I say, "none of that, thank you, no kneeling, it's alright, really, I'm not that important. Clever, and handsome, and very, very cool, but nothing you need to kneel down for." They look more perplexed about getting up than they did about the initial descent. I'm going against the training, you understand. Apparently I'm quite the figure to this private army. Which, considering they seem a courageous and honest sort, I'm alright with.

"You don't look like the pictures," Flavia says.

There's a note of apology about it; sorry for taking us prisoner, even though she didn't know who we were and we arrived in much the same manner as any other thief. I very much want to put her mind at rest. "Well, what pictures have you got, because that could be understandable."

I don't get an answer. Horace interrupts, just can't help himself, "Is the Great Centurion with you? We always hope, but-"

A lot of things come home to me. Facts, definites, things to be sure of. Reality. This reality, here and now, as things stand, comes home to me.

"…Not this time. Sorry."

"It's still the Doctor." Flavia looks disgusted with him, rolls her eyes. "It's still not a bad day."

Slow terror draws over Horace again. "…And I punched him in the nose. I punched the Doctor in the nose. Oh gods, I'm sorry. I'm so sorry."

"On the contrary; your Centurion would have been proud."

It is at this that the current Centurion, the one who's actually in the room , the boss with the shield, he steps between them and me. "Let the man breathe, would you?" Turning back to me, "I take it you've come to see Anna."

No. To see a big machine that can borrow out souls and track them and analyse them and do all sorts of interesting things. Don't tell me I've just spent hours in a cell with excellent views of an artist's impression Pandorica (which, remind me, I have to talk to you about reality in a minute) and I'm in the wrong temple. Actually, really, really don't tell me that, because I'm absolutely sure I got the coordinates right, so if I'm in the wrong place, that means You-Know-Who has been messing me about again, and after the lock-out this morning, her and I are on some thin ice already and-

He's waiting for an answer. "I'd love to see Anna, yes, yes I would."

In the background of all this, behind his questioning and me thinking and ranting and answering, Horace and Flavia have turned their curious attentions to Clara.

It began with Flavia. She said, "And you? Who are you?"

"Clara Oswald. The Doctor and I travel together."

To which Horace replied, "Oh," and both Horace and Flavia lost interest after that. And I can feel Clara wilting. I can feel her silently asking herself why she is 'oh'. What does 'oh' mean, she's thinking. I want to turn round and tell her that it's nothing to worry about. Clara is lovely. It's not Clara they're 'oh'-ing at. Clara is delightful and therefore they will be delighted by her, when they get to know her. It's just that the legionaries have heard a different story. She's not in the legend. Yet. She will be soon enough.

But I can't tell her all that. Can't stop to comfort her. I'm being diplomatic with the Centurion.

Turns out, it's not sensible to leave Clara hanging. She takes matters into her own hands. Literally, actually. I become gradually aware of her little white hands, pressed together, easing between the Centurion and I, and pushing us apart.

"Excuse me," she says, not missing a step as the whole party moves off towards the mysterious Anna, "but I have no idea what's going on here. You all do, and he's pretending he does." (He is me, by the way, I'm the pretender, apparently) "But I'm absolutely lost, so if you wouldn't mind just explaining to me who you are, please?"

For those of you who study my various tales in order that you may learn lessons about how to cope successfully and happily in the universe, that is not good diplomacy.

The Centurion, however, seems to be in a good mood. Or maybe he just likes answering her. If I had a name like Captain Titus Dorica Androcas of the Last Legion, I'd like introducing myself even more than I already do. (I'm the Doctor, by the way… Yeah, that never gets any less fun.)

Clara prompts, "And the Last Legion is what exactly?"

With something that is almost a laugh, "Our more correct name is that of The Pondecai. We are, to be correct, the descendants of the Last Legion, who were the followers of the Great Centurion. Ours is the sacred duty to defend the most powerful weapons in all the known universe, and to keep them from the hands of those who would use them ill."

Clara probably misses a lot of it. It's very strange; the parts I pick up on, the parts that are important to me, those are the parts that have bypassed her completely. Clara skips straight to his last sentence.

Wary, testing him, "That's brave of you. Must put you in the way of some nasty sorts."

"Courage doesn't come into it, Miss. We have the knowledge and the capabilities, and that gives us an obligation."

Oh, I like him. He's got the right idea there. Now if only I could get him to tell me who he got it from…

Actually, this could be the time to talk to you about reality, like I said I would. I'll tell you first what's going to happen to Clara, just so you'll know. She'll give him her name so he can stop calling her Miss. Then, if these Pondecai are as familiar as they seem with me and my story, they'll get into some arbitrary discussion of the role of the companion. He'll respect her, and she'll like that. It'll make her feel better about the whole 'Oh' business.

And meanwhile, I'll tell you a little something about reality.

These are the Pondecai, who are the followers of the Great Centurion, who referred to the Pandorica as their raison d'être. They are Roman legionnaires of impeccable character in space, defending powerful weapons from evil-doers. You will forgive my tone of utter panic when I tell you concisely that they are a pack of Rory-Worshipping-Rories which is wonderful, you couldn't make me happier than to tell me that there was a pack of Rory-worshipping-Rories out there in the universe and that they were in charge of making things honest and safe, you really couldn't. But how? The question is how, because all of those things that they're referring to, the Pandorica, the Roman, the Last Legion, none of that ever happened!

The world ended, and then I brought it back. You don't remember this because you were ended and then you were back. But I remember because I had to live through it (and then get wished back into existence (which is a bit more painful than you'd think (I have to stop these brackets)) Is that enough? One more?) There, closed. But the world ended. The whole Pandorica, plastic centurion, just shy of two millennia, that was undone. Those involved hardly remembered it themselves.

So here, in reality, this reality now that we're living in and I'm talking about, how on Earth do these supposed-Pondecai even exist?

Ponder, then, the riddle of the Pondecai, if you will. I have to stop talking about reality now. We've come to the end of the corridor, and Horace is being called to bring the keys again.

This door we're at now is not a steel-barred-cell-type-door. It's a two-storey tall set of double doors gilded and marble-panelled. They are so big that if you stand close to them, and I am standing close, you could almost miss that the patterns of the marble echo again the sides of the Pandorica. Almost. You could miss it if every turn and circle of that pattern hadn't printed itself on your mind, if you weren't the only person in the universe who could still remember it. It's a joy to me when Horace finds the right key and he and Flavia push the doors aside, apart, away, out of sight.

Beyond them, the décor changes. It becomes clinical, scientific, white and green and steel. A sterile environment for what I'm told is a very delicate instrument. Will its very-delicacy prevent me from lashing it to the back wall of the Tardis like a bank holiday Dad trying to get a flat pack shed home and getting Clara to keep an eye on it on the journey back? No. But I'm told it is, anyway.

That, of course, is provided there's even a delicate instrument here. I could be here to see Anna, who for all I know is Captain Titus' elderly white-haired mother. Don't get me wrong, I'm sure it's a delightful woman that produced such a sterling gent, but I do rather need to obtain some sort of nihilium-analysis technology.

"Doctor," Titus says, and he stands with open arms. "Welcome to ANNA."

Clara's going to ask what Anna means. She is. She's going to ask what we're being welcomed to. She'll do that for me. What she's not going to do is stand there smirking at me, leaving me with no choice but to ask him myself and prove that, yes, I was pretending to know what's been going on all this time. She wouldn't do that to me. Clara's nicer than that.

Her nose is doing that funny, crinkly thing it does when she wants to grin and she won't let herself. It's smug. I don't like it.

"Alright, fine," I sigh to the Captain, "What's ANNA, exactly?"

Flavia passes me on the left, making her way to a sort of plinth. Very large, round, raised up from the floor no more than the height of the average stair. There is a pillar just at the side with some monitors and what looks like a fairly standard calibration system. "Aerobically-Naturised Nihilium Analysis. Soul-photography and extraction from a cellular level."

"Ah," I say. 'Ah' is like 'Oh' when you don't want to be so insulting. Disappointed without being impolite about it. "This whole room is Anna? Big Anna? There's no little portable Anna, then? No sort of Anna-souvenir I can take away with me to show my friends and use to maybe save the universe someday maybe?"

The Captain looks sad that I'm even asking. Forgive me for having a glass-half-full approach. You have to ask. "Nothing like that. I'm happy to offer you unlimited access to this facility but… this technology was a one-off. No chance to refine it. It never got any smaller."

Then I need to get a very good look at how it works before I leave. Sneakily, I move my recovered sonic from my inside pocket to the outside one, so it can hang from my jacket and record what I see. More than that too, it can map the machine we're standing inside, it's controls, what makes it work. It can steal this for me. Borrow. Borrow. Borrow without asking, and you can't exactly return knowledge, but I'll delete the records, so it's still borrowing.

"Does Anna go?" I ask.

Horace moves past, nodding. "She needs a subject, though."

Clara made me admit, when I was trying to be diplomatic, that I was a bit lost. Now that a subject is needed for the workings of a powerful and undemonstrated machine, I slide a step closer to her, hands behind my back, nonchalant. Then, very quickly, I put one of those hands behind her back and give her a good hard shove forward. "Volunteering, are you? Very good, Clara, very brave. Just hop up there where Horace is showing, there's a good girl. Don't worry, perfectly safe, I'm sure. Just like helping out with a magic act. Don't get sawn in half and you'll be alright."

She's still stammering her 'what' and 'no' when she stumbles onto the plinth, and is in position. Horace steps down. Flavia types a few commands I hope the sonic is getting, and Anna activates with a heavy thunk.

Clara freezes, gasping. Utterly terrified, scared to even move, she flicks her eyes to me, but will not speak.

Mere moments pass. Then it starts. It's very small, at first, just a sort of smoky edge along her outline. It shifts like smoke, and is a thousand colours, but all of them are warm and earthy. Reds and browns and deep, rich ambers. Autumn leaves.

"Doctor?" she mumbles, like even moving her lips is too much. The Captain calls over my shoulder that she shouldn't be so scared. But it's not what she wants to hear and so she can't hear him. "Doctor, I'm all fuzzy. What is it?"

"It's you, Clara. All your inside, mind-y, self-y bits. They're out to say hello, that's all."

"Well, can you put them back in, please? I liked them where they were." From the corner of my eye I see Flavia reaching for another button. Very sneaky, very surreptitious, I give her a little signal down by my side to hold her off. "No, don't give her secret signs, Doctor. I can see you. Just put everything back."

"Clara, there's nothing to be scared of. This is just a visual representation. Everything real is still with you. And not just in your heart or in your memory or any of the other stupid places people try to say that yourself comes from, but in all of you. In every single cell, it's right there. That's your life. Everything that makes you Clara, whose initials spell the noise a pigeon makes. It makes your eyes brighter than any other eyes that I know. It makes you talk faster than any other living being." There. The first idea of a smile flashes across her uncertain features. "You are not second best. You are not a mystery or a distraction. The Tardis doesn't hate you."

"She does."

"She doesn't. She just knows a different story, that's all. Now, Clara, what I'm going to say next is very important. Are you listening?"

"Don't have much choice, do I, while I'm stuck up here and you won't put my bloody soul back…"

"Clara Oswin Oswald," I begin. At just the sound of her name, her aura grows. Her nervousness and fear are subsiding. She doesn't feel so endangered or exposed and so she's able to share, whether she knows it or not. It grows, and strains to grow more against her remaining reservations. "You are not now, nor have you ever been, nor will you ever be, 'Oh'."

Another moment's struggle. Then her eyes meet mine through the haze and Clara, delightful Clara in all her glorious blooming loveliness, she blooms, just bursting, and looks around in wonder and awe at her own incredible colours, flashing green and gold amongst the earth tones. Here through the cloud there's a crackle of sound that is her mother's voice, and here the haze momentarily forms two young, playful faces, and Clara ducks as the imprint the Tardis has left on her whizzes past on its way to somewhere incredibly exciting.

She giggles. It is bright as electricity and gives part of her aura the precise texture of a paper bag so crumpled its gone soft. There's a faint and slightly chemical smell of strawberries. I fight to recognize it and then cry, "Opal Fruits! I love Opal Fruits!"

"I like the green ones better," she tells me, sounding happily dazed by it all. She laughs again when the scent changes to sharp lemon-and-lime, and somewhere near her ear there's a big, lazy chewing motion as she recalls getting her teeth stuck together, the sound of the grin that was permanently pinned to her face as a child.

"There." This is all I really wanted. I didn't know that. I thought I wanted the technology, or at least the capacity to recreate it. I didn't. I just wanted this. "I wanted to see you glow." And when I say that, she really starts glowing. I'm not entirely sure what to do with that. Flounder a bit, turn around from her, and isn't it funny how you always get an itch at the back of your neck when something like this happens? "Well, the machine's no good if it doesn't work, is it? I needed a guinea pig."

This time, Clara says, "Oh." Flavia shuts off the machine. By them time Clara's hopped back down, she's grinning again, "That was amazing."

"Obviously I can't let you take it away," the Captain is telling me, "But it's as I said; whatever visitor or prisoner or subject you might want to bring here, I can promise you won't end up in the cell again."

I won't be back. I'll build my own. But then again, I was being diplomatic today, wasn't I? "I appreciate that." And now we have to go. Not that it hasn't been a nice visit since the unfortunate imprisonment incident ended, but we have to. Clara, for all that she's still beaming, still glowing even now that the glow is gone, wants to go. She can't see this herself, but there's something disturbing about having everything that makes you you plucked out and visualized. Even a spirit as intensely beautiful as hers has darker places, and at the very best it's all exposure. She's still at the height now, but later on, when she's alone, when she's back in her jimjams and trying to sleep, I'm not sure she'll be able to.

Autumn leaves. May I never forget she looked like autumn leaves.

I don't explain all this. I say something cheerful and meaningless. 'Must dash' and then a false, borderline facetious excuse, probably.

I get as far as those patterned doors again before I turn on my heel and rush back to the Captain. "No, wait. Wait-wait-wait-wait-why? Why do I have unlimited access? How do you know me, what do I mean here?"

"You are the Doctor," he tells me, looking baffled by my idiotic question, "who gave the Great Centurion the most valuable advice he ever received."

I'm thinking… thinking… "…You'll have to narrow it down for me."

"You told him, as he stood at the doors of the sealed Pandorica, that he would never be able to bear the eternity of waiting at those doors. You made him aware that it would drive him mad. His sacrifice was always willing, and that was always admirable. But you gave him a choice. That makes his sacrifice intelligent. That's what makes it heroic."

"But how do you know all that, it never happened. I mean, it did, but then I took it away again and I'm the only one who's supposed to know anymore."

This doesn't confuse him. Which is really good going, because I myself am deeply, deeply confused. "But you still knew," is how he replies to me.

"Yes."

"And you believed. Even though you didn't see it all, you believed without a doubt that it all happened. The long wait, the Last Legion, the Great Centurion."

"Without a doubt. And I still do."

Then it was real. Isn't that what he's trying to tell me? So long as I brought it back with me, out of nothingness, it's real. I brought it back with the stars. Something of it must have survived. Writings on tablets, drawings on walls, carved Pandoricas. The story still exists so long as there is somebody to tell it, and somebody to listen.

I've told and they've listened. The Pondecai. The descendants of the Last Legion, followers of the Great Centurion.

You can't hug a Roman captain, not in good conscience, so I wait until we're out of the room and then I hug Clara. Tight, but only for a second. Then I stand back and start down the corridor. She's still giddy enough to giggle. "Alright, that's the third one today. What was that for?"

"You have pretty insides."

[Dedicated, like I said before, to the lovely folks over at Rory Williams Is The New Chuck Norris - the least I could do for you guys. You have the prettiest insides on Facebook.]