It was about half an hour later; Celestia's guards had returned Shining Armour and baby Twilight to their parents (who had been waiting in the queue of petitioners at the palace) – the last they'd heard was Shining Armour trying to tell his mother that they'd been attacked by “a stallion with some sort of fire wand” and rescued by Nightmare Moon and Princess Celestia working together. It was clear that Twilight Velvet didn't believe a word of it.
Celestia herself, in the meantime, had temporarily closed the day court (citing 'urgent business') and locked herself into a meeting room with her time-travelling guests.
“Are you alright?” she asked Twilight, once she was sure they wouldn't be interrupted.
“I'm fine,” said Twilight. “Why do you ask?”
“The fur on your face is... somewhat singed,” pointed out Celestia. “It doesn't look serious, but I imagine your eyebrows will take a few days to grow back.”
“...huh,” said Twilight. “I must have been a moment too late with that shield.”
“You know us, Princess,” stated the Doctor, bluntly. “You've met us before.”
“Yes,” said Celestia, “I have.”
“Be careful,” said the Doctor, “telling us about it. Whatever it was, it... well, we haven't been there, yet, so -”
Celestia held up a hoof. “I am aware of the risks, Doctor,” she said. “The first time you and I met – from my point of view – you gave me quite a long talk on the subject.”
“Ah,” said the Doctor. “Very well, then.”
Celestia raised her teacup, and took a sip. “I am... very nearly immortal, Doctor,” she said. “My age is best measured in millenia; and you have popped up several times in those years, and dealt – or helped to deal – with a surprising number of threats over the years.”
The Doctor sighed. “I guess that means I'm going to have a busy time ahead of me,” he said.
“So... you've met us before... but we haven't met you before yet?” asked Twilight.
“In the time of my greatest despair,” sighed Celestia. “You came and offered comfort.”
“Ah,” said Twilight. “But... you've never seen Paradox before?”
Celestia shook her head. “Neither seen nor heard of,” she says. “He seems to be interested in killing you, specifically, Twilight?”
Twilight nodded. “Yes, and I have no idea why.”
“Then I shall keep a very close eye on your... younger incarnation,” said Celestia, promptly. “If Paradox should turn up again before you are able to defend yourself, I will make sure that his attempt fails.”
Twilight sat still for a moment, then stepped forward and hugged the larger alicorn. “Thank you, Princess,” she said.
“It is my duty,” said Celestia, with a slight smile of her own. “After all, your younger incarnation is one of my subjects.”
“Right, now that's arranged,” said the Doctor, “and thank you very much, your Highness, but you know things from our future and we know things from your future, so we really shouldn't hang around and chat for too long, spoilers are a serious problem, after all...”
“Do you know where you are going next?” asked Celestia.
The Doctor stared at her. “Um,” he said.
Celestia smiled slightly. “You are welcome to use this meeting room as long as you would like to decide on your next course of action,” she said. “Or you're welcome to adjourn to the TARDIS, if you prefer.” She paused for a moment, before asking “One more question, Doctor. Is it inevitable that you become that – Paradox?”
“No,” said the Doctor, promptly. “It is not.”
“Very well, then,” said Celestia, standing up. “I have a long queue of petitioners to talk to today, so I shall take my leave. I don't know what could happen to turn you into Paradox, but I do urge to try to avoid it as much as possible, whatever it is.”
Celestia stood up, and turned towards the door.
“Princess!” Twilight jumped up. “Did you – you don't recognise what happened to Paradox?”
Celestia turned back slightly, raising an eyebrow. “He turned grey and went homicidal,” she said. “I've never seen that combination of symptoms in my life. Should I have?”
“Um,” said Twilight. “Maybe... maybe not. It, um, it hasn't happened yet...”
“Then don't tell her about it!” snapped the Doctor. “Spoilers!”
“Um,” said Twilight.
Celestia smiled. “I shall leave you to it,” she said. “Besides, Twilight, I still have to listen to your parent's petition.” She stepped out of the room.
“Never?” asked Twilight, quietly. “But that means...”
“Whatever it means,” said the Doctor, “it's better if we don't discuss it here. For one thing, I don't know who else might be listening -”
“I'm sure -” Twilight began.
“For another,” said the Doctor, “the sooner we're back in the TARDIS the sooner I can try to see if I can trace Paradox's next jump.”
“Oh. Right,” said Twilight. A purple glow gathered around her horn; there was a *pop* and a flash of violet light, and both ponies vanished.
* * *
“It would hardly be very secure if anypony could just teleport in,” said the Doctor, opening the door to the TARDIS.
“I guess not,” said Twilight. “Still, I hope we didn't give those foals too much of a fright.”
“They did seem to think that you were Nightmare Moon come to gobble them up,” pointed out the Doctor.
Twilight winced.
“But I'm sure they'll grow up to be fine, well-adjusted adults,” continued the Doctor, reassuringly, as they stepped inside.
“I, um. I think the blue one may have been Trixie,” said Twilight, nervously.
“Who?” asked the Doctor.
“You remember the Alicorn Amulet?” asked Twilight.
“Oh,” said the Doctor, closing the door behind them. “Right. Well, I'm sure that this little incident had very little to do with that. I mean, what'll she tell everypony? That Nightmare Moon turned up and tried to eat her but ran away when she screamed?” He shrugged. “Nopony would believe her.”
“Just like nopony would believe her if she claimed to have defeated an Ursa Major,” mused Twilight. She winced again.
“That might actually be more believable than chasing away Nightmare Moon,” pointed out the Doctor. “I mean, she could potentially meet an Ursa Major, and anypony can occasionally be really, really lucky. But Nightmare Moon is still trapped in the moon, and everypony can see that.”
“...I feel terrible,” said Twilight.
The Doctor rolled his eyes. “Look, Twilight,” he said. “Whatever Trixie says, or does, or will say, or will do in the rest of her life – it's not your fault. It's not your responsibility. She has free will. She has choice. She can choose her own actions, and she – and she alone – has to bear the responsibility for those actions. Nothing that she's done – or is going to do – is your fault, Twilight. Now. You seemed to indicate earlier that you knew what had happened to Paradox, to make him so, well -” The Doctor waved a hoof.
Twilight nodded. “Yes,” she said. “Discord did the same thing to my friends, the first time we met him; he turned them grey, and made them act the opposite of themselves. I found a way to reverse it, by reminding them of who they had been before with a memory spell...”
“That won't work on Paradox,” said the Doctor. “He's – as I said – made himself immune to any and all forms of change. Injury, age, experience – even a cure. He... he can't be cured unless he wants to.”
“I don't think that will work, then,” said Twilight. “All of my friends fought back when we tried to cure them. Do you know of any way to stop him?”
“Short of throwing him into a black hole?” asked the Doctor. “I don't think he can be stopped, as such. But it is possible to... limit... how much damage he can do.”
“I'm sure we can dig a hole,” said Twilight, mystified, “but why does the colour matter?”
The Doctor sighed, and waved a hoof. “Just think of it as an inescapable prison,” he said. “A place that nothing leaves from, or can leave from, until it evaporates a few billion years in the future... and then all Paradox would need to do is build a new time machine, and he can turn right up again.”
Twilight nodded, uncertainly.
“No,” said the Doctor. “No, that's really not that good an option. You say it was Discord who did it to your friends?”
Twilight nodded. “And... Celestia said that she'd never seen him do it before... so, if it was a new idea at that time, then that must mean... he wouldn't have had much chance or reason to pick on you the first time he was freed, and the second time Fluttershy kept a very close eye on him until...” Twilight frowned in thought. “Doctor, before we continue following Paradox, do you mind if we make a bit of a detour, back to the future? I think I want to talk with Discord, as soon after Tirek's defeat as you can get us without meeting my past self; we might be able to resolve this entirely by preventing Paradox from ever existing at all...”