Vi didn’t look up immediately as she heard someone walk into the room. Only as the steps got closer did she realize that they didn’t sound like they came from Twilight... or from Spike.

“Fluttershy!”

The pegasus turned her head. She was standing on the bottom of the staircase that led up the elevated part of the library’s upper level. Rather than waiting for her to come up, Vi jumped straight down, causing a shriek from Fluttershy as she rushed towards her, hugging her front limb.

“Oh g-goodness.” Fluttershy giggled, wrapping a wing around the filly’s backside. “That looked dangerous.”

“It wasn’t. I cushioned the impact with magic.”

“Oh. I didn’t see it.”

They parted.

“Did you come to visit Twilight?”

Mostly I came to visit you.” Fluttershy smiled.

“... me?”

“Mh-hmh. I heard that you helped Rainbow Dash to a quick friendship lesson.”

Vi nodded. “You were the only one who wasn’t there at the party. So I got to meet everypony else.”

“And do you like them?”

“I like Rarity, don’t like Rainbow Dash. Pinkie I’m not sure of. Applejack seems very humble and honest, but a bit boring to me. And Twilight I like a lot.”

Fluttershy’s smile flickered a bit, but only for a few moments. “Hmmhh. Talking to you is really... I remember now that it’s something special.”

Vi opened her mouth to respond, but closed it again when Fluttershy continued.

“I wouldn’t normally expect... a detailed answer like this to such a question.”

Vi shrugged. “That was the short version. Most answers that are shorter and useful aren’t the truth.”

“Well,” Fluttershy said, “you probably didn’t have the best introduction to Rainbow Dash, I would think. She’s really sweet, normally, um... she just gets carried away, sometimes.”

“I only met them once, except Twilight. All impressions can change.”

Fluttershy nodded. “Are you still Spike’s assistant?”

“Yes.”

“How is that?”

“Careful,” Vi said with a giggle. “Another dangerous question.”

Fluttershy echoed her giggle, not backing down. “That’s okay.”

“It’s a bit annoying. Spike has some requests that seem a bit silly to me. But it’s not much worse than I expected. I plan to keep it like this. Can you not mention any of that to Spike or Twilight?”

Fluttershy nodded. “Of course.”

“But don’t lie. Tell them the truth if you have to.”

That brought another smile to Fluttershy’s face. “I promise.”

“Do you have any ideas of what we could do?”

“I could show you more of Ponyville, if you want to,” Fluttershy offered. “Or, we could go to my place and I could make us a lovely salad, if you’re hungry.”

“I’m just a bit hungry. I’d still like that idea, but, uhm-”

“The animals?”

Vi nodded.

“How are things going with Owlowlicious?”

Vi shuddered. “He’s creepy.”

Fluttershy giggled.

“Smart for an animal, though.”

“Mmmhh.”

A pause.

“So what do you want to do?”

“Can I think for a while?”

“Oh. Sure.”

Vi nodded. Half a minute passed, during which she paced around the room, thinking.

“Okay. Show me around Ponyville.”

“So, what do you think?”

They’d been to Carousel Boutique for a short visit, to the park, to Town Hall, to some of the shops, and to the retirement home where Rainbow Dash had rescued four ponies from a fall which might or might not have been deadly. Now they were standing back in front of the library.

“About Ponyville?”

Fluttershy nodded.

“It seems like a very nice place to live. The town itself doesn’t seem too special, but the ponies do.”

“What makes you say that?”

“Everypony is friendly, and it doesn’t feel like they do it out of obligation. That, and Twilight told me the party in Sugarcube corner had formed organically. That’s fascinating.”

“Mhhh...” Fluttershy bowed her head in agreement. “That happens a lot on weekends. Everypony wants to get together, they’re just looking for an excuse.”

“Everypony except you?”

“Oh, I do join, sometimes... but I don’t like big crowds very much.”

“Not even crowds of ponies this friendly?”

“Not even those.”

“You’re pretty smart, Fluttershy.”

Fluttershy blushed, and short twitch ran through her wings. “Oh, you’re just...” she began but then paused, her gaze refocusing on the filly beside her, as if she was remembering whom she was talking to. “Uhm. I... I guess you aren’t just saying that, are you?”

“I’m not.”

“Oh. Um, t-thanks...” A pause. “There’s nothing wrong with Twilight, is there?”

“Wrong in what way?”

“Oh. I... uhm... I just... I mean, she... she’s...”

“Twilight is one of the smartest ponies I ever talked to,” Vi said, “but that has nothing to do with you.”

“Oh.” Fluttershy sounded relieved. “No, of course not. So everything is going well?”

“I think so. I like Twilight a lot. Actually, I was thinking about what to give her for her upcoming birthday. Rarity mentioned it when we met. Do you have plans for a gift?”

Fluttershy nodded. “I asked Zecora for foreign tea leaves. I know Twilight likes to drink tea, and I think she would appreciate experimenting with something new.”

“Zecora?”

“A zebra shaman. She lives in the Everfree Forest. Vi, I don’t think Twilight is expecting to get a gift from you.”

“I don’t think so, either. Do you have an idea?”

“Um. I’m not sure.”

“Not sure whether you have an idea?”

“Oh.” Fluttershy blinked. “Uhm, I mean no. I don’t have an idea right now.”

“Ponies have this weird habit of never thinking about questions,” Vi said. “Want to come in?”

“Oh, yes.”

Vi rang the doorbell. A few seconds later, Twilight opened.

“Hi you two. How was the trip?”

“Hmmhh... I’m not sure,” Fluttershy said, looking at the filly. “What do you think?”

“I don’t think I know, either. It’s a difficult question, wouldn’t you say, Fluttershy?”

“Oh, yes. Absolutely.”

Twilight groaned. Then all three of them laughed.

“It was nice,” Fluttershy eventually said, and Vi nodded.

“Are you staying for longer, Fluttershy?”

“I think Vi and I were still having a conversation. I’d stay for just a few minutes so we can finish, if that’s okay.”

“Sure.” Twilight stepped aside. “I’ll be downstairs.”

“If I think of something for you, I’ll let you know,” Fluttershy said quietly as they walked to the upper floor. “But, um... you don’t have any money, do you? That makes it difficult.”

“Yes.”

“Although...” they entered the upper level. “You could always tell Twilight where you’re coming from. I’m sure she would appreciate that as a gift.”

“Too early.”

They looked at each other for a few seconds, then Fluttershy sighed.

“Oh Vi, I just don’t want things to turn out ugly. I’m not even sure if... Twilight may still be having doubts. Just taking somepony in like that is... it’s not normal.”

“I don’t want things to turn out ugly, either. I’m doing most of what I can to make them turn out well.”

“Oh... of course.” Fluttershy shuffled her front limb nervously, her wings twitching. “You’re not mad at me for asking, are you?”

Vi shook her head. She took a few steps forward, and Fluttershy leaned down for another hug. It lasted for almost ten seconds, then they parted, Fluttershy now smiling.

“Take care. I’ll see you at Twilight’s birthday.”

Vi nodded. “Bye.”

“Goodbye.” Fluttershy excused herself with another smile, then headed downstairs.

“Vi?”

“Mh?” Vi was sitting on a stool beside the tiny table in the library, as usual busy reading one of Twilight’s suggested books.

“It looks like we’ll have the party in Canterlot tomorrow. Do you want to come?”

Vi looked up. “Definitely. What happened?”

“I got a letter from Rarity.” Twilight summoned a piece of paper, offering it to the filly. “She says she can’t make it, but I’m pretty sure Pinkie will just move the party to Canterlot.”

My dear Twilight,

I am afraid I won’t make it to your birthday party tomorrow, because poor Opal is quite ill. And she is in no condition to make the long journey back to Ponyville.

I do hope you understand

Your friend
Rarity

Vi read the letter, then shoved the book further aside, then read it again.

“Something wrong?”

“Maybe,” Vi murmured. “Twilight, can you promise not to be mad at me if I tell you what this made me think?”

“Alright.”

“It sounds like Rarity is lying.”

“Really?” Twilight sounded skeptical. “Are you sure you aren’t just saying that because of how much you value truth?”

“No. How much does Rarity value truth?”

“I...”

For a while, Twilight seemed to think about the question, while Vi pulled the letter close once more, a frown crossing her face.

“Not as much as you, or Applejack, or I. But she wouldn’t lie without a good reason.”

“Is Opal her pet?”

“A cat.”

“Well, the chance for a cat to suddenly be sick is very low, but we mostly have to look at the probability of anything forcing her to stay, period. That, compared to the probability that something happened which made her lie. I assume the former is more likely, but this letter is evidence for the latter. Do you want to know why?”

“Go ahead.”

“Okay. Firstly she says ‘long journey back to ponyville’. How long is it, an hour by train?”

“About seventy-five minutes.”

“Still hardly a ‘long journey.’ And the second reason is that she is overly respectful and apologetic here. Maybe she feels bad about not attending your party, but if Opal is sick, then she has nothing to apologize for. Both are explained by her feeling dramatic and guilty for lying to you.”

“Yeah, but normal ponies don’t think like that. She can’t attend the party, after I had Celestia offer her to stay in the Castle. She probably feels guilty, even though she can’t help it.”

“Maybe.” Vi bit let lip. “I hope so. But... ‘your friend, Rarity’ is just too formal. Imagine you had two letters in front of you, both written by Rarity, and you knew one was a lie and the other one wasn’t. You take the first, read it, and it says this. You would guess that it’s probably the one with the lie, right?”

“Probably. But Vi, that’s only with two letters where I know one is a lie. That’s not the same thing.”

“Yes, but it updates the evidence from our priors. Okay. I claim the letter sounds apologetic, dramatic, and formal. How much more likely do you think the letter is to sound that way if Rarity is lying than if she is telling the truth?”

“’How much’?” Twilight echoed. “You mean a number?”

Vi nodded.

“Hm. Five times as likely.”

“Suppose you only knew Rarity wasn’t returning, but haven’t read her letter. How likely that she’s lying?”

“Three percent. Why aren’t we counting the letter?”

“We are counting the letter,” Vi said. “Like this: three percent means the odds for Rarity lying are 1 to 33, but the odds of her writing this letter are 5 to 1 for a lying Rarity versus a genuine Rarity. Therefore, the updated odds of her lying are 1 times 5 to 33 times 1, so 5 to 33, or 5 in 38, or about one in eight.”

“... are you sure that’s correct?”

“Yes.”

“Hm.” Twilight sounded skeptical.

“Imagine blue and red water coming down a waterfall. All of the red water reaches the bottom, and only a fifth of the blue water does, the rest gets lost on the way. But, there is thirty-three times as much blue water to begin with. What happens there is very simple and it’s absolutely correct to calculate it that way: multiply the amount of red water with the proportion that reaches the bottom, and same for the blue water. One to thirty-three over five, or five to thirty-three, or five in thirty-eight. Same thing.”

“Makes sense,” Twilight said slowly. “But I know a longer formula that-”

“-P of A given B is P of B given A times P of A over P of B?”

“... yes.”

“It’s the same thing, just much more complicated.” Vi took a breath. “If you ever explain probability to someone,” she said, “don’t tell them the formula. Just explain them the waterfall.”

“The same thing? It sounds longer.”

“It has some absolute values that cancel each other out. If you make up absolute probabilities for Rarity writing the letter if she’s lying and Rarity writing the letter if she’s telling the truth with a proportion of five to one and then plug them in, you’ll get the same result. After a lot more calculating.”

“I see.” Twilight smiled. “Now you’ve taught me something new.”

Vi beamed. “Glad to help!”

“Our result was one in eight, yes? That’s not too bad.”

“Um,” Vi made. “With your odds, yes. I don’t know Rarity as well as you, but-”

“You’d have changed them? Higher chance of lying?”

“No, three percent is fine. But I don’t think she’s just five times as likely to write it like this if she’s lying. More like fifty times. Twilight... I really hope I’m wrong, but nopony writes like this. I really think she’s lying.”

“Well,” Twilight said, “we’ll see when we’re there.” She took Rarity’s letter in her grasp, reading it one more time. “... hm.”

She folded it back in, putting it somewhere out of sight.

“If she’s been telling the truth, don’t tell her we’ve been speculating.”

Vi nodded. “I promise. Unless she asks me.”

“I think we can establish that this exception always applies,” Twilight said with a chuckle, but she got serious momentarily. “Actually... don’t tell her either way. Even if she’s been lying.”

A day later, all six of them stood in front of Canterlot Castle.

Twilight looked at the others, who nodded, then she pushed the door open.

“Surprise!”

And Rarity, who had been standing right in front of the entrance, and who was wearing a yellow dress, flowers on her tail, and a giant hat, brought a hoof to her head and literally fainted.

“Wow,” Twilight murmured. “Looks like you were right, Vi.”

“Yup,” Vi murmured, sounding all but happy. “Looks like it.”

“Err, whaaaat exactly are you guys talking about?”

“Rarity was lying to us,” Twilight said to Pinkie Pie. “Probably.”

“Oh. But why would she lie?”

“We can ask her once she wakes up.”

“Let’s get her inside,” Fluttershy suggested. Everyone murmured their approval, and Twilight floated the unconscious body into the Castle hall. While still in the air, Rarity opened her eyes, causing Twilight to quickly put her down.

“Hi again,” Pinkie greeted, her voice not quite as cheerful as normally.

“Rarity, have you been lying to me?”

“I... well, I’m... I... I’m... that’s...”

No-one interrupted the silence as Rarity’s voice broke. On shaky hooves, the fashionista stood up, taking a deep breath.

“Yes, I did. I’m very, sorry, Twilight.”

“Why?”

“Well, b-... because, because Fancy Pants, he... he invited me to the Garden Party on this afternoon, and that’s... it’s the prime event after the Grand Galloping Gala, you see, and so-”

“Oh, Rarity...” Twilight sighed. “You could have just told us.”

Vi’s eyes shot daggers at Rarity, and Twilight’s compassionate tone only seemed to make her more upset.

“But... I didn’t... I didn’t know you would-”

“DIDN’T KNOW?!” Vi shouted. “COME ON! Come on! COME ON! You didn’t think she would understand? Your best friend wouldn’t understand that you want to go to a high... argh, whatever party? COME ON! HOW COULD YOU POSSIBLY HAVE THOUGHT THAT WOULD BE A GOOD ENOUGH REASON TO LIE?”

“Vi-” Applejack began, but Vi cut her off.

“You lied! You LIED! You LIED TO YOUR FRIEND FOR SOMETHING THAT WAS OBVIOUSLY UNNECESSARY DID YOU THINK ABOUT IT FOR EVEN FIVE SECONDS HOW COULD YOU DO THAT?”

“Vi,” Twilight now said, “get your magic under control.”

The filly’s horn had begun to glow during her outbreak, and now the silver hue intensified, until she cast a beam against her own outstretched limb, which was cast in a quickly fading light for a few seconds.

“Um,” Fluttershy said, “c-can we all be f-friends again n-now, please?”

“Folks of yer age shouldn’t talk to grown-ups like that, misses.” Applejack gave the filly a stern glance. “I don’t like lyin’ as much as you do, but I know better than to shout at an older pony.”

“Vi has the mind of an adult,” Twilight said. “She has as much right to shout at somepony as we do. And we don’t shout at others.”

“Are you really making this about me?”

“It’s about both, Vi. Rarity shouldn’t have lied, but you shouldn’t have started screaming. Look at what that did to Pinkie Pie. And Rarity.”

The pink pony in question stood completely still with moisture glistening in her eyes, while Rarity seemed to be in utter shock.

Vi took a deep breath. “I’m sorry, Pinkie Pie.” She closed her eyes, literally grinding her teeth for a few moments.

“... and Rarity,” she pressed forth, almost intelligibly.

“Yes,” Rarity said, “that seems to be in order. And I am sorry to all of you for having lied without a good reason. Rude as it may have been, I suppose what Vi said was correct.”

“Yeah,” Twilight responded, causing another round of murmured agreement.

“Can you still make it for the garden party?” Vi asked, causing everypony to turn towards her in surprise.

“Pardon?”

“You already did one stupid thing,” Vi said, “as we just agreed on. The lesson now shouldn’t be to do more stupid things, like missing an important event for a party which we could easily have without you... or reschedule.”

“Says the pony who just shouted at a bunch of adults,” Rainbow Dash remarked.

“I’m sorry,” Vi said, keeping her voice steady, “but that doesn’t have anything to do with Rarity, does it?”

“We already moved this party here-”

“Exactly,” Vi cut her off. “We already moved it here. Therefore it has zero bearing on the decision at hoof. If it was better to attend the Garden Party before, then it is better now. And if it wasn’t better I’m sure Rarity wouldn’t have lied.”

“Why is that your business?” Rainbow asked, her tone now sounding aggressive.

“Stop that,” Twilight weighed in. “Just because Vi made a mistake doesn’t mean what she’s saying isn’t true. Rarity, if this event is important, I think Vi’s right. You should go.” She turned to the others. “Right?”

“I think so, too,” Fluttershy was first to agree.

“Rainbow, if you had a one-time meeting with the Wonderbolts, would you let it go to attend my birthday?”

“Er... I guess when you put it that way, nope.” Rainbow gave a nervous chuckle. “Sorry, champ,” she added in Vi’s direction.

“Friends are important, too,” Applejack said with a frown. “But it’s your call. I s’pose, Rarity.”

“You should do what makes you happy,” Pinkie said quietly. “If you want to be at this Garden Party thing, then it’s no good to be at Twilight’s party instead. Partying with unhappy ponies is no fun.”

“So.... you really think I should go?”

“It’s okay, Rarity. We can talk more later.”

“Wow, Twilight. First you get me a seat at the Castle, and now this. I... I don’t know what to say.”

Twilight giggled. “It’s okay, Rarity, really. Just go and have fun.”

Rarity nodded. “Well then.” She picked up the hat which she had lost earlier, making sure it still looked to be in proper condition.

“Um, Rarity? Is this my dress?”

Already in the process of leaving, Rarity froze in her step, slowly turning around.

“... yes, it is. I was going for an elaborate design, you see...” She nodded towards the sketch on her clipboard. “... but with all these invitations, I never got the time, so...”

“So there were several parties leading up to this one?”

Rarity nodded.

Twilight chuckled. “Looks like you’ve been doing really well for yourself.”

Even though Twilight’s tone had been friendly, Rarity blushed, looking uncomfortable. “Are you ... are you going to wear it anyway?”

“Nah, I’m good. Nothing wrong with celebrating your birthday naked. I’ve done it for the last nineteen years.”

“Heheeh...” Rarity gave a nervous laugh. “Of course.” She grabbed the dress in a gray cloud as if to remove it, but changed her mind momentarily. With a rather awkward smile, she excused herself, heading for the entrance.

“Are you going to throw me out?” Vi said as soon as she was gone. “Please don’t throw me out!”

“Throw you out?” Twilight looked at the filly, giving a smile. “Of course I’m not going to throw you out. You’ve been a lovely mare... filly... since you moved in, before now.”

“Wasn’t that just a week ago?” Rainbow asked cynically.

“Six days,” Vi said.

“Still. I’m not throwing you out just because you misbehaved once.”

“You could do something to punish me,” Vi suggested.

Twilight gave her another one of those looks where it wasn’t clear whether she was amused or serious.

“Maybe. We’ll talk about it later.”

Author's Note

Twilight was in a tunnel.

From ahead, she could hear the distant rustling of leaves, the low scratching of nails against stone. But she could also see a glimmer of light, of freedom. Behind her, there was nothing but darkness.

A vague sense of discomfort took hold of her as she took cautious steps towards the light. The soft wind that blew through her mane, casting the sounds from beyond her vision, it seemed like a promise, the promise of wonder, of a secret.

The sound of splashing water made her wince. As her eyes flickered down, she could see that her left hoof had sunk into a hole in the soil of the tunnel, where a small puddle was forming. She pulled it out with a grunt, quickening her steps forward.

As the walls parted beside her, Twilight breathed a sigh of relief. Her gaze darting around frantically, she made for the cover of trees to her left. The wind was stronger here, waving through the leaves and branches, but it wasn’t enough to cover up the screeching coming from somewhere close... from somewhere near...

Through thick branches whose color faded at her gaze, Twilight could spot the creature ahead. Black and red it was, with leathery wings and long claws whose nails were scratching across a wall to its side. The sight of the wall would seep through the branches, but only where it was touched by the demon’s body, leaving her at a loss to discern what structure it belonged to.

When Twilight closed one of her eyes, the trees would lose their transparency, and the sight of the demon would disappear. It was smart to hide herself, Twilight thought as she made steps to her left, trying to get away, away... if she stared at it too long, would it feel her gaze? Did it know?

The tunnel was closed. She would be unable to go back. Only to hide could be her goal, to escape sight. Around her, the forest seemed to come to life as her steps took her farther away, and she could hear the chirping of birds, and the silhouettes of smaller creatures that ran across the edge of her vision. It all was animated by the wind, the wind that blew through the leaves, through her mane, through her head, that woke her up to the tired sight of a wooden roof.

Twilight blinked, feeling a mixture of fear and intrigue as her mind roamed through the fading images of her dream. Rolling around in her bed, she felt for an article on her nightstand, calling it to her in a purple cloud. Without losing time, she scoured through the notebook’s sheets, coming to a halt at the page past her latest entry. Hastily, she put the quill on the top of the page, proceeding to write down everything she could still remember.