Twilight Sparkle woke up on a completely normal day in her library home in Ponyville. She yawned and stretched as she rose, and she dutifully made her bed before heading downstairs. She paused along the way and rolled her eyes as she spotted Spike's bed with his sheets a strewn and tangled mess. No matter how many times I tell him, she thought to herself as she tidied up after him. "Spike!" she called out.
There was no answer, and Twilight called again on her way down the stairs. Still no reply. Now where could he have gotten to? He didn't try to get a head start on our errands without double-checking the errand checklist again, did he? she wondered.
Once she was at the bottom of the stairs, Twilight trotted toward the kitchen. As she passed along the bookshelves, something caught her eye. No, that can't be right. That's crazy, she thought, assuring herself that she must have imagined it. She made it five more steps before she turned around to double check. Sure enough, there it was: The Myth of Sisyphus by A. Camel in the middle of the historical fiction section. "What are you doing here?" Twilight asked as she pulled the book off the shelf and carried it over to its proper place in the philosophy section on the far side of the library.
The bookcase assigned for philosophy was, to Twilight's astonishment, completely full. "When did this happen?" she wondered aloud. The ornithology and sociology bookcases on either side had an open shelf each, of course, but splitting sections in the middle of a bookcase was such a haphazard way of organizing, and the extra signage alone would require an entire afternoon to plan. Not to mention, the next re-shelving wasn't scheduled for another month. "No. There must be another book out of place in here that's taking up space. I just have to find it."
From A Treatise of Pony Nature to Zen and the Art of Skywagon Maintenance, everything in that bookcase belonged there. Twilight double- and triple-checked it. She even went to the card catalogue to confirm it. Twilight stared at The Myth of Sisyphus. "How did you end up without a space on the shelf?"
"Twilight?"
"Gyah!" Twilight wheeled around. "Oh. Spike. You startled me."
"You were talking to the books again. Are you okay?" Spike asked.
Twilight laughed. "I'm fine. Where have you been? I was looking for you."
"What do you mean? I've been here all morning. I even asked if you needed help with that book you've been carrying around, but you didn't answer me."
"Oh. I'm sorry, Spike. I didn't mean to ignore you. I guess I was just distracted." She showed the book to Spike. "Do you know how this ended up in historical fiction?"
Spike looked at the book. "I didn't even know we had that one. Maybe it's somepony's personal copy they left here by mistake?"
"No, that can't be right. I checked the catalogue and it definitely belongs to the library. But the philosophy bookcase is completely full and every book that's in there is supposed to be there. So we have a book with no place to put it. I can't just let something like this sit in the wrong section. What if somepony needs this book? They won't be able to find it, and then I'll be a bad librarian for not keeping the shelves organized and—" Twilight was interrupted by a growl from her stomach.
"Maybe you should take a break and eat lunch," Spike suggested.
"Lunch? But I haven't even had breakfast yet. What are you talking about?"
"Uh, Twilight. . . You've been carrying that book back and forth around the library all morning. Are you sure you're okay? This isn't gonna be like that time you lost your favorite quill, is it?" Spike patted Twilight on the shoulder while leading her toward the kitchen.
"That was a one-time thing, Spike. And you know how much I liked that quill." Twilight groaned. Sure. Literally turn the entire town upside down one time and nopony ever lets you forget it. She sat down at the table while Spike set about preparing her something to eat. She was still carrying the book with her.
"Well I guess since you skipped breakfast, do you want oat flakes?"
"For lunch? Are you serious?" Twilight thought for a moment. "Well, technically, it would still be breakfast since it is breaking a fast. But then again, doesn't every meal do that? I suppose if I were constantly snacking all day, it wouldn't be. . ."
"Oat flakes it is."
"But if I eat breakfast now, then what happens to lunch? And dinner? And—" Twilight's attention snapped to something new. "What is that?"
Spike looked where Twilight was pointing. "Um. A door?"
Twilight face-hoofed. "I can see that. What is it doing there?" She got up from her seat and took a closer look at the door set in the wall of the kitchen. "This was never here before."
"Are you sure about that?"
"Am I sure?! I think I would know if there had been a door here since we moved in last year. Where does it even go? There's nothing but tree trunk behind this wall."
"Isn't that just the pantry?"
"No. No. The pantry is over there." Twilight pointed to another door, on the other side of the kitchen.
Spike went over and opened the pantry. Sure enough, it was filled with their usual store of foodstuffs, all precisely organized and labeled. "Huh. So it is." He came back over to Twilight. "So maybe this is just a second pantry?"
"We don't have two pantries." Twilight squinted at the door. It was an ordinary-looking door, made of the same wood as the tree that made up her home. Is it possible we've had this door all along and I never noticed it? she thought, supposing that maybe it blended into the wall so well she simply hadn't seen it.
Spike reached for the handle. "Let's open it and see—"
Twilight swatted his claw away with the book she was still carrying. "We have no idea what's on the other side. This calls for careful study and observation. Can you run to the town hall and get a copy of the library blueprints?"
"Blueprints? You want to look at the library's blueprints? How about you come with me? It's a nice day outside; maybe you just need some fresh air."
"Spike, I don't have time for your nonsense. Just go and get the blueprints. I need to stay here and keep an eye on the door in case anything strange happens."
Spike sighed, and headed for the front door, muttering under his breath, "Something strange has been happening all morning. I guess while I'm at the town hall, I can at least warn them that another lost-quill incident is in progress. . ."
Twilight began her study of the door by taking basic measurements. Its width and height were consistent with the other doors in her home. A sample of the wood fibers from an inconspicuous area was likewise indistinguishable under a microscope from samples of the other doors. There were no obvious scratches or tool marks on the door, its frame, or the surrounding wall. And there was no lock of any kind on the door. For all Twilight could conclude, this door had been installed with everything else at the time of the library's construction.
What if, when Spike gets back, the blueprints show the door has always been here? she thought. Faced with the distinct possibility that she may be unable to reject the null hypothesis—that the door had somehow escaped her notice for over a year—Spike's suggestion of simply opening the door began to sound entirely reasonable.
Twilight reached for the handle.
There could be anything in there!
She quickly pulled her hoof away.
"Well, it couldn't be anything. It would have to fit inside the available space. Although, I guess it could be a staircase into some underground room. For all I know, what's inside there could stretch out underneath the entire town." Twilight narrowed her gaze at the door. "What secrets are you hiding?"
Stepping closer, Twilight scanned along the edges of the door, trying to find a gap to peek through. Alas, the door was fit snugly within its frame, and even along the bottom, she couldn't see anything.
She leaned in and pressed her ear against the door, but could hear nothing.
Twilight took a step back and eyed the handle. Again, her hoof reached toward it, hovering an inch away.
"Maybe I should knock first." She raised her hoof toward the center of the door then stopped and shook her head. "What am I thinking? It's not like we have somepony else living here that I somehow also didn't notice for more than a year."
Her hoof moved back to the handle, this time making contact. Just in case, she held The Myth of Sisyphus at the ready.
Twilight turned the handle and opened the door.