Some days, Rainbow Dash liked to go on a leisurely flight around Ponyville. It didn’t really fit the showy persona she liked to project, but sometimes it was nice to just take a break to appreciate being a pegasus. Not that there was anything wrong with being an earth pony or a unicorn, of course; she just couldn’t imagine personally going her entire life without the feeling of the wind in her feathers and nothing beneath her hooves. But it wasn’t weird or anything that most ponies could and did. She wasn’t racist. Honestly.
There were in fact several reasons why she never discussed these flights with anypony.
On this particular afternoon, having just finished such a flight, she decided to head over to the library to see if Twilight had any good adventure books she hadn’t read. As much as he loved the Daring Do series, they just weren’t as good the fiftieth time through as they were the first. Hopefully Twilight could recommend something new.
However, when she burst into the library in her typical boisterous fashion, she found it to be quite empty. And in retrospect, she should have expected that. Now that she thought about it, she had seen Twilight during the flight. She had been in a field on the outskirts of Sweet Apple Acres, apparently talking to herself. And then she had flashed green flames and turned into some earth pony stallion whose name Dash couldn’t remember. Twilight was probably still busy being that stallion, and he’d have needed to head back pretty soon after Dash saw him to have made it on hoof by now.
Wait, that wasn’t right. Twilight did not normally turn into other ponies. But that green flame did look familiar . . .
“Buck!” Dash swore rather more loudly than she had intended. Twilight must have been replaced by a changeling.
“Rainbow! What are you doing here, and why are you swearing like that in front of Spike?”
Twilight, or rather somepony who appeared to be Twilight, had just returned, with Spike riding on her back. “I was, um, here to borrow some Daring Do books.”
“But you own the entire series.”
“That’s right! Thanks for reminding me. And I swore because I, uh . . . stubbed my hoof on something.”
“There is nothing that you could possibly stub your hoof on within five feet of you.”
“Yeah, well, I stubbed my hoof on the floor. I think it needs smoothing. And look at the time! I need to go . . . watch the butterfly migration with Fluttershy.” Dash took off so quickly that quite a few books were ripped off their shelves by the wind. It was actually quite impressive that she could fly through a doorway at those speeds without hurting herself.
“But the butterfly migration isn’t for two months!” Twilight called after her. By the end of the sentence, Dash wasn’t even visible. “What is going on with that pony?”
“I don’t know,” Spike said, “but do you have to treat me like such a baby? I already know not to use those words. I remember the last time you washed my mouth out with soap just fine.”
And the two of them commenced to bicker.
As was so often the case, Applejack was out bucking apples. And then she was suddenly coughing on a giant cloud of dust. When it cleared, she saw Dash standing at the end of a set of furrows where she had apparently skidded to a stop. “What in tarnation has ya in such a hurry?”
“Prove that you’re Applejack!”
“What?”
Dash approached to well within AJ’s personal space and flared her wings threateningly. “Prove that you’re Applejack.”
AJ recoiled in confusion. “Cain’t you see me?”
“Not good enough. Tell me something only Applejack would know.”
“Ya secretly love Hinny of the Hills, ya started writin’ a book about a pegasus who ya swear ain’t you getting into the Wonderbolts but got bored after twenty pages, and ya punch like a little filly.”
“Wait, who told you I punch like a filly?”
“Ya showed me at the Runnin’ of the Leaves last year. Now will ya tell me what’s goin’ on?”
Dash sagged as the readiness to attack left her. “Twilight’s a changeling.”
“Ya’re joking, right?”
“I saw her change. She was out in one of your fields, and then there was green fire, just like when they invaded during Shining Armor’s wedding, and then she was some stallion. I think I’ve seen him in town, but I don’t know him.”
“Ya seriously saw Twi change?”
“Would I say one of my best friends had been replaced by a soul-sucking monster as a prank?”
“Well, why are ya just standing here talking ta me then?”
“Because I don’t know what to do! Changelings travel in swarms, don’t they? They could be all over Ponyville! I don’t even know how to find them. I need a plan, but I don’t know how to make one. Twilight would have a plan . . .”
“Hmm . . . Ah bet Pinkie could help. She knows everypony. She oughta be able ta tell if somepony’s been replaced, if she’s still there.”
“How many days until Big Macintosh’s birthday?”
Pinkie had no need to pause for thought. “112 days. Did you forget? I won’t tell anypony, I Pinkie Pie swear.”
AJ spoke to Dash. “She’s Pinkie.” Returning her attention to Pinkie, she responded, “No, ah was just testing ya. There are changelings in Ponyville, and we needed to know ya really were yourself.”
Pinkie gasped. “Changelings?! A test?! Did I pass? Who am I?”
AJ sighed. “Yes, ya passed. Ya’re Pinkie Pie.”
“What a relief! I like being Pinkie Pie. I’m not sure how to be anypony else, anyway. Though it might be fun to try . . . but what if I didn’t like who I was? Wouldn’t that be terrible? And what if—”
“Pinkie!” Dash interrupted. “We need your help. Twilight’s been replaced, and we have no idea how many other changelings might be in Ponyville. Can you find the ponies who have been replaced?”
“Did you try asking Twilight?”
“That thing in the library is not Twilight.” Dash objected. “Why would we ask the enemy? What do you expect her to tell us?”
“Actually,” AJ said, “she has a point. The changelin’ might give something away. And the others might mess up if they’re worried about bein’ found.”
Dash nearly kicked the door off its hinges as she charged into the library. “We’re on to you! Confess!”
Spike looked up from his sweeping in alarm. “How did you know that last time I helped Rarity find gems, I ate three of them, even though she only said I could have two?”
Applejack entered in a more sedate and reasonable manner. “We didn’t. Some o’ us are just overeager.”
Pinkie hopped in just behind AJ. “Hiya Spike! Is Twilight here?”
“Yeah, she’s in the loft, studying.” He resumed sweeping.
The three mares headed up the stairs to the inevitable confrontation.
“Did you break the door?” they heard behind them as Spike noticed the effects of their entrance. “Just look at this thing! I am not fixing that.”
The three walked faster and pretended not to hear.
The loft had no door to kick open, but Dash did her best to recreate her entrance into the library anyway. “Confess now, and maybe we’ll go easy on you!”
“Huh? Confess to what? What are you talking about?”
If Dash was the angry cop, Applejack was the calm cop. “We know ya’re a changeling. We can find what ya did with the real Twilight and who else y’all have replaced with or without yer help—”
“I’m not a changeling! Why would you even—oh. You must have seen Gabby. I’m the real Twilight, and I can explain.”
“A likely story!” Dash interjected.
“I haven’t even started to explain yet! You could at least give me a chance to talk before disbelieving what I say.”
The crazy cop jumped into the interrogation. “Wait! This really is Twilight! She’s telling the truth.”
“Thank you, Pinkie. I’m glad somepony trusts me.”
“If ya’re the real Twi’, why is there a changeling with yer face, and why ain’t ya concerned?”
“Because Gabby’s trustworthy. Princess Luna herself vouched for him.”
“How do you know she’s not a changeling?”
“No changeling could raise the moon. They aren’t attuned to the heavens and they aren’t remotely strong enough. A changeling who replaced Princess Luna would have to convince Princess Celestia to take control of the moon without arousing any suspicion, despite her knowing that Luna was working on rehabilitating changelings. It just wouldn’t work.”
“But why does this ‘trustworthy’ changeling look like ya?”
“I’ve been training him to impersonate me. Sooner or later I’ll need to start making regular royal appearances, even though most of them will be unimportant. Luna suggested I train Gabby to take my place sometimes, so I don’t need to leave Ponyville as often.”
“Oh. I guess that makes sense.”
And that was the end of that crisis.