Disclaimer: Doctor Who belongs to the BBC and Worst Witch belongs to Jill Murphy; you know the drill

Feedback: Always appreciated

AN: The final chapter of this story; I wanted to get this storyline finished before the new series started and we saw what the Thirteenth Doctor is like for real.

Anyway, hope you've liked this little crossover.

The Great Doctor

"Ah, Mildred," Miss Cackle smiled, looking in approval at the young witch as she walked into the headmistress's office. "I apologise that we had to skim over it earlier, but I trust that the trip to Hollow Wood was satisfactory?"

"It was… interesting," Mildred nodded. "I mean, there was a brief encounter with a… hypno-pillion?"

"That was real?" the Doctor looked curiously at the young brunette. "And you dealt with it?"

"Found the counter-spell and… well, took it from there," Mildred shrugged in her usual self-effacing manner.

"Good for you," the Doctor smiled, Miss Cackle nodding in approval even as she stayed behind her desk. "Always impressive when you deal with the unexpected twists."

"…Thank you?" Mildred shrugged uncertainly at the headmistress. "Actually, Miss Cackle, I was just… I mean, I'm grateful that you're going to answer my questions, but won't HB… well, won't she wonder about this? I mean, the way she was looking at the Doctor…"

"I can deal with Hecate's questions in their own time, Mildred," Miss Cackle said reassuringly. "Give me time to come up with a suitable explanation and I can assure her that no slight was intended, and in a worst-case scenario… well, I don't like to use it under normal circumstances, but memory-dust will deal with things."

"Net result is that you need to let us worry about how certain parties will react and you just focus on satisfying your curiosity," the Doctor grinned.

"Right…" Mildred said, looking uncertainly between the two women before her mind seized on the most confusing term of the morning's conversation. "So… well, I had a bit of time to think, and the thing I don't get the most is… well, why were you falling through the air like that?"

"Fell out of my time machine," the Doctor shrugged. "It happens."

"You fell out of your time machine?"

"The old girl had a bit of a breakdown after I regenerated and needed to get me out of her while she repaired herself," the Doctor clarified. "Drastic way of doing things, but she didn't have much of an alternative; I let off a lot of energy last time and it really threw things off inside her."

"You mean… you let off a lot of energy when you… changed?" Mildred said, indicating the Doctor uncertainly. "I mean… you mentioned that regeneration process, and you said you were a man before…"

"True, but the actual process is extremely complicated to describe even for us, and if you're thinking of asking me about the differences between the genders, don't bother," the Doctor shrugged. "It's too early in this body for me to give you any clear answers on that front; obviously I'm feeling a bit top-heavy all of a sudden, and this new body seems a bit light between the legs, but nothing obvious beyond that apart from stuff that could be put down to me finding my feet in this new body."

"I… see," Mildred said, deciding that she didn't want to ask for any more on that particular topic; there was idle curiosity, and there was risking getting an in-depth explanation on what it felt like to have a… thing versus not having one. "So… talking of unusual terms… what were you talking about when you mentioned a Valeyard?"

"To give you the appropriate context, it was the name assumed by the individual who was the manifestation of all the evil that exists within the Doctor," Miss Cackle clarified.

"Manifestation of…" Mildred began uncertainly. "You mean… he was like Mr Hyde?"

"Good analogy," the Doctor smiled grimly. "And the basic principle's pretty apt; from everything I've learned about him, the Valeyard was the manifestation of my dark side."

"Barring the fact that the Valeyard and the Doctor were physically separate entities instead of them alternating control of the body as one turned into the other," Miss Cackle pointed out. "The Valeyard's exact origins are unclear to us even now, but all sources agree that he came from the Doctor's future, created under undisclosed circumstances, who travelled into the past to use his knowledge of the Doctor to benefit his own efforts to take the Doctor's life for himself."

"He… wanted the Doctor's life?" Mildred said uncertainly. "But… if he was from the Doctor's future… and he killed the Doctor now…"

"He was evil, ambitious, and utterly insane; it's not a good combination even if you aren't as brilliant as me," the Doctor clarified. "Add in our ability to travel in time, and… well, let's just say I have a feeling that his arrogance is the only reason I'm still here."

"His arrogance?"

"He needed to let me know he was winning," the Doctor said, a solemn expression on her face. "Sometimes that's all the time you need to turn things against your enemy."

"Indeed," Miss Cackle said, smiling slightly in acknowledgement at the Doctor before looking back at Mildred. "In any case, during my last regeneration, I essentially triggered a similar split to the one that may have created the Valeyard to create Agatha, while also ensuring that she and I would regenerate into children rather than remaining the age we are and suppressing our memories into the bargain in the process."

"You did?" Mildred looked at Miss Cackle in surprise. "Why?"

"To see if I could change her," Miss Cackle said, suddenly looking particularly weary at that confession. "It was the kind of arrogant mistake you can only make when you have had centuries of being right behind you and think you can achieve something impossible just because you want to believe it's impossible for everyone else…"

"You know, I do get that I made a mistake the last time I was home; you don't have to rub it in," the Doctor smiled at the headmistress in an exaggeratedly exasperated manner.

"OK…" Mildred said, aware that there were several questions in that last statement but reluctant to ask any of them right now; if Miss Cackle was as old as the Doctor, Mildred suddenly doubted she could ever fully understand the motives for some of the things that might have prompted such a comment. "So does that mean Agatha's… is she more like your clone than your sister?"

"Not exactly," Miss Cackle replied. "Agatha basically is my sister, in that we were distinct personalities from the beginning but were genetically identical; she just… had greater potential to go the other way than I did."

"She did? But… when I went through the Mists, you were-"

"She was the focus of my darker instincts; that did not mean I had none myself," Miss Cackle clarified.

"That was one of the reasons I've always had trouble with the idea of the Valeyard," the Doctor put in, the other woman now sitting on the edge of the desk as she looked thoughtfully between Mildred and Miss Cackle. "When you see the worst of yourself in physical form, it can be… difficult… to recognise the difference between the need to do what that part of yourself is capable of, and the idea that you could enjoy what that part of you is capable of."

"Pardon?"

"I have promised myself and the universe that I will never be cruel or cowardly," the Doctor said, her tone solemn as she looked at the young girl. "The Valeyard represents the part of me that lets me be cruel when I am certain that I have no other choice but to break that promise, but he lacks the part of me that understands when I can't do something."

"Uh… what do you mean?" Mildred asked, uncertain if she wanted to hear the answer to this question even as she knew she had to ask it.

"There are times when I have to kill people," the Doctor said bluntly. "I would always make that my last option… but the Valeyard would not only make it his first as soon as it occurred to him, but he would enjoy doing it because that is what he is."

"Ah," Mildred nodded, looking uncomfortably around herself before she decided to ask a less morally conflicting question. "So… if magic is real… how can aliens be real too?"

"Oh, the one doesn't preclude the other, Mildred," Miss Cackle smiled. "It's just that magic is… well…"

"To put it in a related context, you're aware of the basic idea of three dimensions of space, right?" the Doctor put in.

"You mean… length, breadth and width, right?"

"Exactly," the Doctor nodded. "Anyway, there's also the fourth dimension of time, which you obviously know of but can't travel through on your own, and the fifth dimension, which is what we call the Time Vortex; it's what allows our people to travel in time in our time machines."

"OK…" Mildred nodded uncertainly.

"Magic and such powers are essentially the ability to access the higher six dimensions of reality that exist beyond the fifth dimension of the Time Vortex," the Doctor continued. "Not everyone can do it, of course, but those with the right physical and psychological potential are able to tap that power and use it on our level, utilising those powers to accomplish feats that should be impossible on our level."

"Our level?" Mildred asked.

"Think of it as though we were simply drawings on a piece of paper," Miss Cackle explained. "We would be flat beings with no concept of height or anything beyond the ability to go left or right, without even an understanding of the concept of up or down; if someone came along who could lift us up, we wouldn't even understand such a thing was possible."

"I… see," Mildred nodded. "So… magic is just us drawing power from these higher dimensions of reality?"

"Basically, yes," the Doctor nodded. "You get the ability to do things that shouldn't be possible from your perspective, but from the higher dimensions it's really pretty simple."

"I… think I get it…" Mildred nodded tentatively. "So… it's like that thing I heard Arthur C. Clarke write? There's no real difference between science and magic when you get to a certain point?"

"Always liked that view," the Doctor nodded.

"OK… so I've been getting a bit of an idea on how things work in the world of magic compared to… well, stuff I'd read before… but how do things work… out there?" Mildred asked. "I mean, Star Trek and Star Wars… how do they compare to what's really in space?"

"Take out the Force, the lightsabers, and the lack of currency for the Federation and you're basically there," the Doctor replied. "Obviously it changes depending on what time period I'm visiting, but generally you'll find an interesting mix of people trying to get along and the particularly aggravating races who just think everything would be better if they were in charge or everyone else was dead."

"Ah," Mildred said.

"Which is one reason the Doctor works with UNIT, I believe?" Miss Cackle smiled.

"UNIT?"

"Unified Intelligence Taskforce," the Doctor grinned. "Set up in the 1970s by an old friend of mine, UNIT is basically responsible for dealing with alien incursions in this part of the world; America's done its share, of course, but their anti-alien groups tend to be more about just blowing things up where UNIT's been willing to let me talk things over a bit more recently."

"Oh," Mildred said. "So the government does know about aliens?"

"Certain government officials, anyway," the Doctor clarified. "Obviously not everyone can know everything, but the right people know enough to know that there are things out there to beware of, as well as people like me to help protect them."

"Uh… that reminds me," Mildred said, pausing in thought for a moment. "What you said earlier about knowledge being spread out… what was all that stuff you were saying earlier about someone called Sabbath?"

"Complicated," the Doctor and Miss Cackle replied simultaneously.

"Essentially," the Doctor continued, "at one point, when my people were… cut off from the wider universe, knowledge of subjects such as magic that we had kept suppressed for millennia was able to escape into the wider universe. For a time, as I was the only one of our people still available to take action, I tried to organise the new holders of such knowledge so that they could protect the universe in our absence, but that effort was interrupted by a man called Sabbath, who thought that he was a better candidate for acting as Time's Champion than I was."

"Did he ever give a clear reason for that?" Miss Cackle asked. "I heard about the mistakes Sabbath made later on in your encounters with him, and I understand why you had to oppose him beyond the moral issues, but I was never really clear on why he thought he was better than you…"

"He had these ideas about how Time worked that didn't actually match the reality of it," the Doctor said. "He thought time travellers created alternate timelines rather than time being a relatively fixed constant, and hence saw me as a disruptive influence who just made reality worse every time I went anywhere."

"I… see," Mildred said. "And time doesn't work like that?"

"Let's just say it takes a lot of effort to make time split in the way he was worried about and leave it at that; further details would just be confusing without an in-depth knowledge of temporal mechanics."

"I get it," Mildred nodded in understanding. "So… What happened to Sabbath?"

"It turned out that he was being manipulated by another group who had their own agenda regarding the structure of reality," the Doctor explained. "Once his masters' true goal was revealed, he sacrificed himself to deliver a significant blow against them, and that disrupted their plans so that they ran out of power."

"Right…" Mildred nodded. "So when you said your people were cut off… does that tie into why you said something about needing to bring your people back after you lost your memory?"

"Good memory, Mildred," the Doctor nodded at the young girl before her expression became more solemn. "That was… a difficult period of my life; let's just leave it at that."

"Of course," Mildred smiled at the older woman in sympathetic understanding, recognising the signs of a potentially difficult topic, before another thought suddenly came to her. "Hold on; if magic's all about the higher dimensions, where do the founding stones fit into this?"

"It channels the raw energy of the magic and filters it in a manner that will allow the students here to properly process it," the headmistress explained. "Essentially, we use ancient technology to act as conduits to the higher dimensions that give us magic."

"Technology?" Mildred repeated in surprise. "Witches were able to make technology back when Cackle's was built?"

"In a loose sense," Miss Cackle confirmed. "The process of creating a founding stone is… well, suffice to say, the ancient witches knew many secrets that even my sisterhood have yet to fully unlock even after this long."

"Something to look into in the future, anyway," the Doctor noted with a smile, before her expression faltered. "But that depends on me getting the old girl back…"

"And that is where we come in," Miss Cackle smiled, looking at Mildred before turning to the Doctor. "I assume you still have your key on you if nothing else?"

"Right here," the Doctor confirmed, pulling what looked like a standard Yale key out of a pocket.

"That's the key to… your time machine?" Mildred looked at it in surprise.

"Nothing wrong with keeping things simple," the Doctor smiled, looking at the key with an affectionate smile. "I've tried a more exotic-looking key, but there's something to be said for simplicity."

"In any case," Miss Cackle said, "regardless of its appearance, it retains a link to the Doctor's ship, which the three of us can use to bring the TARDIS to this office once it has finished rebuilding itself."

"Will it be ready by now?" Mildred asked.

"It's a time machine, Mildred; we give the old girl a time and place, and she can be back here as soon as she's ready even if it took her centuries to regenerate," the Doctor smiled. "Admittedly, last time I did something like this I tried using block transfer computations and made a few mistakes, but-"

"We shall be fine, Doctor," Miss Cackle said reassuringly before she turned to Mildred. "If you would take our hands, Mildred?"

"Our?" the Doctor looked at the headmistress in surprise.

"You have the same degree of magical potential as any Time Lord if you learnt to channel your mind appropriately, Doctor; you simply lack the natural mental focus to achieve it on your own outside of exceptional circumstances," Miss Cackle explained.

"Like how I had to learn it?" Mildred asked.

"Essentially," Miss Cackle nodded.

"I don't have the time to spend the next few decades learning how to get my mind thinking the right way-"

"Simply reflect on your past instruction and that will suffice, I am sure," Miss Cackle smiled. "I trust you remember Odoyle's lessons if nothing else?"

"Odoyle?"

"A leprechaun who gave me some interesting lessons in his world's equivalent of magic a long time ago," the Doctor smiled, as she accepted the offered hands of the other two women. "Let's see how this goes…"

"Simply focus on your link to the ship, Doctor, and I shall reach out to it," Miss Cackle said, smiling reassuringly at Mildred. "As for you, Mildred, just think of Earth."

"Earth?" Mildred repeated.

"The Sisterhood have been able to summon the TARDIS to us when on our homeworld, and in this case we have the additional asset of the Doctor's link to the ship to draw on," Miss Cackle explained. "You will provide a tie to this planet that will ensure where and when the ship will return to us, while the Doctor focuses on the ship and I instigate the transfer itself."

"Right," Mildred nodded, taking a deep breath as she settled back and tried to focus her thoughts on anything Earth-related that she could think of; the sights from her various holidays with her mum, some of the locations she'd flown to while practising her broomstick work, just spending time with her friends…

She didn't know how to define the subsequent surge of power, but for a moment, Mildred felt like she had access to all the raw potential she'd only been peripherally aware of when she was in the presence of the founding stone, followed by a strange wheezing, groaning sound that she couldn't identify. As the moment passed, Mildred opened her eyes to find herself staring at a large blue box that had suddenly appeared in the middle of the room, which put her in mind of a public phone box, except that it was blue rather than red and only had a few windows at the top rather than several windows all over the doors and walls.

"Are you… sure about this?" Mildred asked, looking sceptically at the blue box as she released her grip on the hands of the other two women. "That… doesn't look like a time machine…"

"Oh, she'll surprise you," the Doctor smiled, standing up and patting the box affectionately as she looked at Mildred. "I'd invite you along-"

"No."

"Pardon?" the Doctor looked at Miss Cackle in surprise.

"Mildred is a child, Doctor," Miss Cackle said firmly. "An unconventionally talented girl, to be sure, but she is still a child; she will not be leaving the planet to go off… Rassilon only knows where with you!"

"As I was about to say, I have learned from past experience not to allow anyone on board full-time if they're too young," the Doctor noted, before looking back at Mildred with an apologetic expression. "It's not that you don't have the right potential, but I'd just worry too much about you at this point even if I was fully confident in my new identity."

"It's… all right," Mildred shrugged, uncertain how to feel about Miss Cackle's defence and the Doctor's own dismissal. "I'd… probably just do something stupid anyway…"

"And why would you think that?" the Doctor looked at Mildred with a soft smile. "Because you have some trouble with your spells? Well, there's a saying that I feel is appropriate here; if you judge a fish by its ability to climb a tree, it's going to spend its life thinking it's an idiot."

"So?"

"So don't think of yourself as stupid just because you take longer to master new spells than certain other people in your year," the Doctor said, crouching down slightly to look Mildred reassuringly in the eyes. "Considering that you're starting from scratch where everyone else has been receiving some kind of training from their parents before coming here, from what I've heard from Ohila here, I think you're doing rather well. Besides, academics mean little in the long run; take it from the man- sorry, woman- who only scored 51% on the second attempt of my final exams."

"Really?" Mildred asked, looking at the Doctor in surprise.

"Of course," the Doctor shrugged. "Academics are important, I grant you, but you shouldn't get so caught up in striving to get them that you miss out on what really matters. Besides, from what Ohila tells me, you've got what matters most in the world; the mind that can improvise when put on the spot, unlike certain people who shall remain nameless who think they're smart because they stick to the rules and focus on remembering raw facts over thinking about how to use them."

"…Thanks," Mildred said at last, smiling and giving the Doctor an impulsive hug.

"You're welcome," the Doctor said, returning the hug before stepping back and opening the door of the blue box, pausing to look at Mildred with an affectionate smile. "Just one last thing, Mildred."

"What?"

"When the stars are in the right place, listen carefully… and some day, before you're very much older, you might hear the answer to the greatest question in the universe."

With those final cryptic words, the Doctor closed the door behind her, followed by a repeat of the earlier wheezing, groaning sound as the light on the top glowed while the box itself faded away, leaving no trace of its presence.

"What did that mean?" Mildred looked curiously at Miss Cackle.

"A rumour I heard once," Miss Cackle smiled. "A rumour that, after so many centuries of secrecy, there will come a time and a place where, under the right circumstances, children whose hearts are in the right place can learn the answer to the First Question."

"The First Question?"

"The Question hidden in plain sight since the beginning of the universe, asked since the beginning of time and never truly answered," Miss Cackle explained, looking at Mildred with a soft smile. "Specifically, 'Doctor Who'?"

"'Doctor Who'?" Mildred repeated uncertainly, before the true implication of that statement hit her. "You mean… you don't know the Doctor's name?"

"Nobody does any more," Miss Cackle acknowledged. "There are rumours, of course, ranging from the Doctor adding syllables to her name to hide from Death to it simply being hard to pronounce in English or that the head of the Doctor's family disinherited the Doctor and decreed that the original name should never again be spoken, but in the end, we just don't know what her name was before she adopted her title as her name, and it is unlikely she will tell anyone directly."

"But that rumour-?"

"Who can say?" Miss Cackle smiled. "As the Doctor has observed more than once, the day we know everything is the day we stop."

"Good point," Mildred said, smiling at the thought of being part of another secret world on top of the magic that had become part of her life since that fateful day Maud crashed into her balcony. "Do you think we'll see her again?"

"That's a hard question to answer, Mildred Hubble," Miss Cackle replied, looking at her young student with a slight smile. "But I can promise you this; if you need aid in the future, the Doctor will be an option for you to call on."

Looking at the place where the blue box had been, Mildred was suddenly struck by the thought that she had once again been exposed to a secret world that so few people truly knew about, this time a world of aliens and time travel on top of magic and witchcraft.

Her world had just become so much bigger than it had become even after her first meeting with Maud, but Mildred couldn't regret this strange sequence of events any more than she could regret meeting Maud in the first place.

Even if she never met the Doctor again, Mildred was certain she'd remember this moment for a very long time…