Twilight Sparkle was just getting some bookkeeping finished when she heard the doorbell ring. "Just a minute," she called, as she tabulated the final numbers, making sure everything was in order. Finally, she looked up to an empty library.
"Huh," she said, and didn't know quite what to do for a moment.
First, she went up to the door and looked outside. Had somepony poked their head in, only to leave? Not that she could see - the streets outside were empty.
Well, that was a little strange! But it wasn't worth thinking too much about, Twilight thought. Maybe she'd only imagined the bell that time. However, on her way back in, she noticed a hat hung up next to the door - Applejack's hat - and when she returned to her desk, she noticed her logbook was open to a blank page. Now this was suspicious.
"Hello?" she asked the room, though not really expecting a reply, so to say. After that, she closed the book, and took a step back, observing. It seemed these unusual events struck when she wasn't paying attention. If she could only see it when it occurred...
There! The book was open again! She tried not to react too strongly, but instead crept slowly towards it, hoping to catch it in the act and maybe figure out what was going on. She was about a leg away from it when she was stopped by something pressing against her barrel. She looked down, seeing nothing, and so glanced up again, and saw a quill running itself against the page. She gasped! Not the page!
Twilight wanted to put an end to this affront to her logbook, but she was again stopped from moving forward. This gave her time, thankfully, to notice that the quill was not just animating itself chaotically over the paper, but writing in a messy, if legible, hoof.
She was just barely able to catch the end of it before the ink fizzled away:
Hey Twilight, it's me, Pinkie!
... Pinkie?
Twilight groaned, "Pinkie!"
The quill wrote:
Sorry!
"What's even happening right now?" Twilight asked. "Where are you? And why are you writing with invisible ink?"
I'm invisible! It was an accident! Sorry!!!!!!!!!
Twilight swept the quill away from the page with an aura, just to stop Pinkie from writing those exclamation marks forever. She tried to take a deep breath. "Okay. You're invisible. And this was-" deep breaths "- an accident. Okay. What do you - what do I - what do you want me to do, Pinkie?"
The writing resumed, but only once Twilight let go of the quill and allowed it to return to the page.
I don't know! I thought you'd have some idea???
Twilight sighed, but stopped it from becoming another groan. As hard as it was to believe in the moment, this was not the weirdest thing Pinkie had ever done. She just wished it had not come on the tail of a long list of comparably weird things, each more difficult to predict than the next, and all a quest and a half to deal with.
"Okay," she said. "Okay, I'll help. I just have to find some anti-invisibility spell and cast it on you." She was just about to search her index when she realized the error. "Um, wait, Pinkie. Is there anything else you can tell me about this? Like how it happened, or any other details?"
She watched the quill scrawl across the page at ferocious speed, regaling her in an unbroken, rapidly disappearing sentence that could only have come from the hoof of one Pinkie Pie. It began somewhere with a blindfold, ran through the myriad events of the day, and eventually came out the other side with an actually useful detail:
then I ran into you and oh, yeah, I can't make any sound either! Isn't that weird?
"Okay, okay, that's good enough, Pinkie," she said. "I think I got the gist. Now just... wait here, I'll see what I can find."
After what must have been nearly an hour of searching, Twilight managed to find an anti-concealment spell, which would remove both invisibility and inaudibility, in some dusty old tome with half the pages still sealed together. Perhaps the lack of need for these spells was a good thing, really.
After some discussion over the logbook, Twilight managed to convince Pinkie to stand in the center of the library foyer, so that the spell wouldn't be fouled up by surrounding objects, while she charged it - and had her wear Applejack's hat, to make for a better target.
But it did foul up, almost instantly after she fired it. Not only was Pinkie Pie not visible, but the hat had gone invisible, too. Only seconds passed before a set of hoofprints appeared around the floor - in a sense. Really, the floor disappeared, as if painted so by the hoofprints, and this invisibility spread outwards like creeping frost, such that moments later only the soil beneath it was visible.
Some letters appeared on the logbook, just long enough for Twilight to read:
Oh no!
... before that, too, disappeared, along with the quill, and the ink bottle, and the desk, and the floor under the desk, and the books on shelves nearby
"Oh, this is bad," Twilight said, and repeated for good measure, "This is bad!"
Was it the book? That damned book! She searched its pages, and others, for some answer - rushed upstairs to escape the creeping curse - but the pages too were fading away. She discovered with horror that her own hooves were transparent, and losing colour fast. There wasn't much time to fix this before - before - she dared not imagine it! And she didn't have time, anyway!
Another spell, then. A solution was necessary, but she'd settle for a delay, or a workaround, or anything to keep her from disappearing altogether. Finally she found one, and committed it to panicked memory just as the book faded away.
She cast it, and saw light, then -