Celestia screamed in pain as a lance of cyan magic struck her from the sky. Her wings failing, she fell like a rock through the hole that Nightmare Moon had left in the castle roof, leaving the dark alicorn to cackle triumphantly over the city.
Though injured, however, Celestia was not defeated. Her earth pony endurance had her back on her hooves mere moments later.
“Oh, dear sister,” she said, her horn glowing yellow. “You have given me no choice but to use – these.”
A panel on the floor glowed and slid aside, and the Elements of Harmony raised themselves into view. Laughter sat in its proper place, a blue crystal, hovering above a stone platform on the upper row.
* * *
Below, in the basement, Twilight sighed with relief. She had been in time. She felt the Elements activate, first protectively around Celestia, and then she felt the wave of magic as they launched a beam of rainbow power against the combined might of Luna, Princess and Monarch of the Night, and the Nightmare in her head.
And then, while that massive font of harmonic energy was present, she teleported back to the castle doorway, where the Doctor was waiting.
“You... said you wanted to yell at me about something?” she asked. “I'm not – quite exactly sure what, but...”
“It's not the right time,” said the Doctor, watching the silhouette of Luna appear on the moon. “Right now, you need to talk to Celestia. I'll yell at you when we're back when you came from.”
“...talk to Celestia?” asked Twilight.
The Doctor rolled his eyes. “Surely you remember,” he said. “Celestia said that in her time of greatest despair, you came and offered comfort, which quite honestly sounds like an absolutely wonderful thing to do. Now, she's just banished her sister to the moon, this is her moment of greatest despair, so you can go in there and offer comfort!”
Twilight squealed and backed off a few steps. Then she turned about and ran back into the castle.
* * *
Celestia was sobbing as she placed the Elements back into storage. She didn't hear, at first, the clip-clop of hooves on the floor.
She did hear the voice. “Princess Celestia?”
“Leave me,” she said, without looking up.
“I, um, I don't think that's...” The voice trailed away.
Celestia looked up, to see who would bother her in her time of grief. She saw a purple pony, saw the horn, saw the wings – and suddenly Celestia was standing up on all four hooves, bacjing away from the stranger, with her wings half-unfurled and her horn glowing yellow. “You will NOT replace her!” she hissed.
“What?” asked the purple alicorn. “No! I wouldn't even try to -”
“Then why are you here?” asked Celestia, not relaxing her threatening stance in the slightest. “Why do you arrive when I've just lost my sister forever?”
“Um. It's... it's not going to be forever,” said the smaller alicorn, nervously.
“Do not give me false hope,” snarled Celestia. “Even if it were possible to return her from the Moon, she would still be homicidal.”
“It, um, it does work out in the end...”
“And HOW could you KNOW that?” screamed Celestia.
“Um. I'm... from the future?” The purple pony gave Celestia a nervous grin. “And I've met Luna, there. She's a, a good friend. And completely non-homocidal.”
The yellow glow around Celestia's horn faded, and she looked up at the other alicorn. “If I find that you are lying to me...”
“I'm not!” squeaked the alicorn, nervously.
“Are you familiar with a blue outhouse?” asked Celestia, sharply.
“It's not an outhouse!” said Twilight, quickly. “It's, alright it looks like an outhouse, but it's what the Doctor calls a TARDIS...”
“...alright,” said Celestia, folding her wings. “Perhaps you really are from the future then, and in all likelihood you will go back there, shortly. In which case I have only one further question to ask. How long?”
Twilight blinked.
“How long until my sister is returned to me?” asked Celestia, sharply.
“Oh! Um. There was this, um, this prophecy I read in a book once...”
Celestia raised an eyebrow.
Twilight cleared her throat and sat straight. “On the longest day of the thousandth year, the stars will aid in her escape, and she will bring about night-time eternal.”
Celestia made a strange squeak. “Night-time eternal?” she asked.
“That part didn't happen!” Twilight said, quickly. “I mean, she tried, but -”
“I think that's quite enough, Twilight Sparkle,” said the Doctor, marching in behind Twilight. “We do not want spoilers, and you have said too much already.”
Celestia's eyes widened slightly. “Twilight Sparkle...” she said, very, very quietly.
“Your sister will be back, Princess,” said Twilight, as she stood up.
“Well done, we've established that,” said the Doctor. “Now, shall we leave before you say something you shouldn't and make this a worse mess than it already is?”