Author's Note
While this story is mainly set in the CDRR universe of my previous fanfictions for that property, familiarity with them isn't really necessary to enjoy the story 
Prologues
PROLOGUE: PONYVILLE
"I don't get it," muttered Twilight Sparkle, scratching the side of her head with one forehoof as she, Rarity, Fluttershy, and Rainbow Dash sat around the Cutie Map. "Why would the map call all of us, then only send out Applejack and Pinkie Pie?"
"It has been behaving a bit oddly since you and Starlight got it working again," observed Fluttershy.
"Which wouldn't have been needed if she hadn't messed it up in the first place," Rainbow added, then looked around. "Where is she, anyway? I haven't seen her in a few days."
"She went with Trixie to Fillydelphia to help with her show," said Twilight with a look of concern. "I'm still not really sure how I feel about those two palling around."
"Well, it is their choice," said Rarity. "Perhaps they'll motivate each other to stay out of trouble."
"Yeah, or help each other get into it," Rainbow quipped, causing Twilight's expression to darken more.
"That's not really fair," Fluttershy admonished her. "After all, they both... huh?" The yellow pegasus's shortened words were quickly followed by a yelp of surprise as a... something... appeared beneath her. It looked almost like a hole in empty space, which she immediately fell into.
"Fluttershy!" the others yelled in unison, diving for their friend, but they were too late. The hole had vanished as soon as she'd fallen into it.
"What happened?" asked Rarity.
"Where'd she go?" asked Twilight simultaneously.
"I dunno," snarled Rainbow, staring at the spot Fluttershy had disappeared from, "but I'm willing to bet on who does". She turned to Twilight. "Where's Discord?"
"Why ever do you ask?" came a disembodied voice from Pinkie Pie's empty seat. It was filled an instant later by the form of the draconequus. "Did I miss something?"
Rainbow flew directly into Discord's face. "Where's Fluttershy?" she demanded.
"I was just looking for her myself." The Lord of Chaos grew genuinely concerned. "Is something wrong?"
"She's gone!" cried Rarity a bit too dramatically, even for the situation.
"We were sitting here talking when..." Twilight paused, trying to come up with the right phrase, "a hole in reality, for lack of a better term, just appeared under her and she fell in. It disappeared before any of us could get to her to help".
"Yeah," added Rainbow with a suspicious look, "just the kind'a thing that'd have your mismatched prints all over it".
"While I can't honestly disagree with your assessment," said Discord, "I assure you I had nothing to do with it. I had just gone by her cottage... we were supposed to meet for lunch... and when she wasn't there, I thought perhaps she'd come here".
"Likely story," Rainbow continued to glare at him dubiously. "You sure you didn't do it?"
"Cross my heart and hope to fly; stick a cupcake in my eye," Discord pantomimed the words of the Pinkie Promise as he recited it, even conjuring a cupcake and shoving it into his left eye for added effect. The cupcake stayed obediently in place, a red iris appearing on its base.
"You don't know anything about it?" asked Twilight, earning her a look from the draconequus that was supposed to be dejected, but seemed more comical with one eye replaced by a cupcake. "I'm not accusing; you yourself just admitted that something like what happened would be right up your alley."
Discord thought a moment; his right eye and the cupcake blinked. "Well, I have been sensing some instability in other parts of the multiverse lately," he informed them. "I was starting to worry... well, never mind what I was starting to worry about; I don't think that's it. Anyway, I didn't mention it to you or Celestia because it had remained far removed from Equestria's reality - at least until now."
Twilight considered this, then turned to the remaining ponies. "Rarity, go ask around town if anyone's seen Fluttershy in the last few minutes or another one of those holes. If that doesn't get any answers, head on to Zecora's place and ask her. Rainbow, you're our perimeter; fan out and search as much area as you can as quickly as you can. Call in the weather team... heck, call in the Wonderbolts to help if you're able." The alicorn suddenly found herself with a military helmet on her head and a corncob pipe issuing bubbles sticking out of her mouth.
"I do so love it when you take charge," Discord quipped.
Twilight spit out the pipe, then shook her head to remove the helmet. "Discord and I will stay here and study the area where the hole appeared, perhaps see if we can replicate it. Hopefully Pinkie and Applejack will get back soon so they can help search, too."
The unicorn and pegasus turned to leave, but Rainbow turned back for a moment. "Hey, Discord?"
"Hmm?" Discord's snakelike tongue wrapped around the cupcake and pulled it into his mouth, leaving an empty hole. He chewed, swallowed, then thumped his chest with his paw, apparently causing his left eye to roll back up into place.
"Sorry for pointing the hoof at you so quickly," the pegasus said sheepishly. "It's just... well, I was hoping it was you, 'cause I know you wouldn't let Flutters get hurt..."
"Thank you, Rainbow Dash," Discord said sincerely. "Even a backhanded vote of confidence from you means a lot."
Rainbow grinned a little, nodded, then her form was replaced by a rainbow streak toward the door as she took off to start her search.
PROLOGUE: NEW YORK CITY
Gadget Hackwrench Maplewood looked around at the assembly of her fellow Rescue Rangers. It occurred to her that perhaps she should straighten up her workshop a little before presentations like this; it was a little crowded. She noted two were missing. "Where's Dale and Foxglove?"
"Out gathering acorns for a new recipe Monty wants to try," answered Nathaniel, Tammy's boyfriend. Though he'd now been with the team nearly two years, he was technically still the newest Ranger, unless one counted the formation of the Canine Squad.
"Oi saw 'em head out as oi was comin' in," added the aforementioned bushmouse, Monterey Jack. "They should be back in a blink or so, if ya wanted to wait."
The blonde inventor shook her head. "That's okay; the Canine Squad are spending the day with Dr. Drake, and I can't bring them up here anyway, so I'll just tell them later." She swept one arm out and stepped aside, revealing what appeared to be a rodent-sized old style television set with a radar dish atop it. The screen displayed several columns of letters and numbers, mostly green but with a few yellow and one row in red. A keyboard was situated in front of the screen. "Well, here it is!"
"It's, uh, great, Gadj," said Tammy shakily, exchanging a confused look with Nathaniel beside her.
"Wow," squeaked Zipper, the fly perched on Monty's shoulder looking equally confused.
Chip, the team's leader and Gadget's husband, tipped his fedora back just enough to scratch his head. "No offense, sweetheart," he said a little nervously, "but... what is it?"
The genius mouse closed her blue eyes and shook her head with a grin; she knew she'd forgotten to say something. "This is the Dimensional Rift Detector and Analyzer," she announced, "or DiRDA, for short. After our experiences with other realities - that Acmetropolis place Professor Nimnul accidentally zapped us to and the two incidents with those Heartless creatures - I started getting more curious about other dimensions, so I built DiRDA both to watch for another potential threat like the Heartless and to see if there might be naturally-occurring portals to other worlds. I've actually had it up and running for a few weeks, but I had to run a lot of calibration tests to make sure it was working".
Gadget indicated the monitor with one paw. "When DiRDA picks up a dimensional rift, it's location - in latitude, longitude, and elevation compared to sea level - as well as its diameter, when it was detected, and how long it remained open are displayed here." Her tone grew a bit more serious. "As you can see, there've been quite a few, and they're getting more frequent. None of them so far have been any reason for concern, though." She pointed to one of the green rows. "This one from yesterday stayed open the longest, at point five-three-eight seconds, but it was only point four millimeters in diameter and close to the bottom of the Laurentian Abyss, the deepest part of Earth's oceans." She pointed to another. "This one was the biggest at point nine-one meters; it opened this morning for point zero-two-six seconds in near-Earth orbit above Indonesia."
The other Rangers gathered closer to the device. "Why are some of 'em different colors?" asked Monty.
"Oh, the colors indicate their proximity to headquarters," Gadget explained, then pointed to the single red line. "This one, two days ago, was in the Ranger Tree itself - in the kitchen pantry, if my calculations are right."
"WHAT?!" the others yelled at once.
"You didn't think that was important?" Chip asked incredulously.
"Oi think we'd wanna know if holes into other dimensions are openin' in our beds, Gedjit-luv," added Monty.
Gadget shook her head dismissively. "It wasn't in anyone's bed; it was in the kitchen," she said calmly, then slid her finger toward the end of the line. "Also, you can see here that it only stayed open for point zero-zero-three seconds, and this S in the diameter column stands for 'subatomic', too small to be accurately measured." She shrugged. "I was a little surprised DiRDA picked it up at all."
As the other Rangers calmed down, Chip resumed analyzing the various readouts. "Have you found any sort of pattern to them?"
"As far as when and where they appear, no," Gadget shook her head. "I have found that they all have two things in common, though: they're always perfectly circular, which is why I started measuring their size in diameter, and they're always exactly perpendicular to the pull of gravity, though whether they're facing up, down, or both is impossible to determine without direct observation."
"I'm almost afraid to ask," Tammy put in, "but how can they be facing up and down at the same time?"
"Well, I can safely presume each rift has a corresponding rift somewhere else in the multiverse," explained Gadget. "When I say it may be facing both up and down, I mean that something could enter the top of one and come out the bottom of the other, and vice-versa." Her teammates looked more confused. "Say you dropped a nut toward the top of one on our side, and threw a ball at the bottom of it simultaneously. If it's facing one way or the other, one won't go through; if it's facing both ways, the nut will come out the bottom of the corresponding rift and the ball would come out the top. Assuming gravity works the same way on the other side, the nut would continue to fall in the other universe, while the ball would be caught by that universe's gravity and fall back through the top of that reality's rift, causing it to come back out the bottom of ours. If someone in the other reality did the same thing, it would have the same effect in ours, unless we did it at the same time, in which case the objects might collide in the rift itself..."
Before Gadget's rambling could build up steam, the device began beeping insistently. "Oh, it's picking up a rift!" Gadget announced, excitedly scrolling through the readings. "It's still open!" she cried, pointing to a red line at the bottom of the readout. She looked again and sighed. "Strike that; it just closed." She then studied the numbers more closely. "One point six-eight meters?! That's the biggest one yet, and it stayed open for four point nine-three seconds!"
"That's long enough for something to come through," Nathaniel pointed out nervously. "Where was it?"
Gadget muttered to herself, doing the calculations as she read. "Latitude forty point seven-eight... longitude minus seventy-three point nine-six... altitude..." her eyes widened. "Ohmygosh, that's in Central Park, less than a quarter-mile northwest of headquarters and about ten feet off the ground..."
Chip suddenly spun on Monty. "Which way did Dale and Foxy go?!"
The Australian mouse's look was grave. "Northwest..." As one, the rodents and insect bolted for the hangar and the Ranger Wing to check on their absent friends.
Dale and Foxglove were stuffing the last few acorns they'd collected into a sack bigger than either of them. "Whew!" the red-nosed chipmunk wiped sweat from his brow. "Think that'll be enough?"
"I hope so, cutie," the bat replied. "That bag's already too heavy for me to try to fly with."
"No problem; I can drag it..." his words were cut off by a loud crashing sound, like several branches breaking. "What was that?!"
She shook her head. "I don't know, but it sounded close."
"Didn't your sonar tell ya nothin'?" Foxglove arched one eyebrow and smirked; Dale smacked himself in the forehead. "That's right; it only works when you make the sound."
"Right; c'mon," she jumped into the air and did a quick loop-de-loop, then caught Dale by the shoulders with her feet and glided toward where the sound had come from. They quickly came to a cleared area about ten feet high with a pile of tree limbs on the ground. Swooping down, the pair found, sticking out of the pile, a horse's head. At least, it was similar to a horse; the muzzle was too short and curved wrong, appearing more like a stylized carving of an equine than an actual horse. More obviously, it was bright yellow with a pink mane.
The creature opened its blue eyes and glanced around, a little dazed. "Oh... what happened?" it asked in a soft, distinctly female voice. Its eyes then fell on the two Rangers and it smiled. "Oh, hello little friends. Can you tell me which way Ponyville is?"
Bat and chipmunk looked at each other, then back to the equine. "Ponyville?" asked Dale. "What's that?"
"Isn't this the Everfree Forest?" She now looked and sounded more worried.
"Not sure what that is, either," Foxglove told her, "but this is Central Park."
The horse's eyes widened. "Isn't that in Manehattan?"
"Yup," Dale grinned, pleased to finally be getting somewhere, but Foxglove rested a wingtip on his shoulder.
"She said Mane-hattan," the bat pointed out, "not Manhattan; I'm not sure they're the same place."
Dale shrugged. "Maybe that's just what horses call it?"
Further discussion was cut off by the buzzing of twin battery-powered motors approaching. The yellow horse yelped and tried to sink further into the woodpile.
"Don't worry," Dale reassured her as Foxglove flew up. "That's just the rest of our friends; they probably heard your fall, too. How'd you get up there, anyway?"
"I... I don't know," she replied. "I was sitting and talking to my friends one second, and the next, I was falling through the branches."
"You fell through a dimensional rift, I think," Gadget explained, approaching with the others. "After my device detected it, we came out here to make sure Dale and Foxglove were okay."
"Who?" The horse paused a moment then shook her head. "Oh, you mean them."
"You didn't even introduce yourself, dummy?" Chip admonished his fellow tamias.
"I was a little distracted by the fact that I was talking to a yellow horse with a pink mane," Dale retorted with a growl.
"We're the Rescue Rangers," the blonde mouse said to the horse. "I'm Gadget; this is Chip, Monty, Zipper, Tammy, and Nathaniel, and you've already met Dale and Foxy."
"Pleased to meet you," the horse smiled. "My name's Fluttershy. Maybe you could help me get home?"
"We'll do our best, Miss Fluttershy," Chip told her, tipping his hat. "First, though, we should get you out of there."
The female squirrel, Tammy, stepped forward as the boys started shifting the fallen branches. "Are you hurt? I'm a trained medic."
"I don't think so," Fluttershy answered. As she felt the weight of a particular branch leave her back, she stood tentatively. Her body was the same yellow as her head, and her tail the same pink as her mane. These, to the Rangers, were not her most distinguishing feature, nor were the three butterfly markings on each of her flanks... far from it, in fact.
"Hoppin' horsefeathers," Monty cried in astonishment, "you're a pegasus!"
Fluttershy glanced over her shoulder at one wing. "Well, yes." She looked around meekly. "I'm sorry if that's a problem..."
"It's not a problem," Chip tried to explain. "It's just..."
"Pegasus-us-es aren't real," Dale blurted.
"Neither are leprechauns," Tammy pointed out with a knowing grin.
"Or spell-casters," added Nathaniel, sharing a similar look with Foxglove.
Monty felt the urge to add "or genies", but he couldn't explain why.
"Remember, guys," Gadget reminded, "Fluttershy here is from a completely different reality than ours".
The pegasus looked confused. "My friends Twilight and Discord would probably know more about that than I would," she said. "As for pegasi, there are lots of us back in Ponyville, and even more in Cloudsdale. I don't know what a leprechaun is, but unicorns cast spells all the time; so do alicorns."
"Alley-whats?" asked Monty.
"I've heard the term before," said Nathaniel, "combination of unicorn and pegasus, correct?"
"Actually, they have traits of earth ponies, too," Fluttershy corrected. "There are six - um, five of them." She glanced around nervously, hoping they either wouldn't catch her slip or simply not question her about it. She tried to stretch her wings, then winced as a stabbing pain shot through her left shoulder.
Before the pegasus could say anything, Tammy hopped onto her back and gently felt around her shoulders. "Hmm... I think there's some swelling in the left wing joint... seems like it compared to the right..."
Fluttershy turned her head to give the squirrelmaid a concerned look. "Is it bad?"
Tammy shook her head. "Best I can do is guess; trying to figure out pegasus physiology is way outta my league." She looked toward Gadget. "You know if Flash took his radio with him?"
"One way to find out," the inventor replied. "We should probably get Fluttershy back to headquarters, anyway; we're lucky no humans have shown up to check out the noise."
"I've heard of humans," Fluttershy said brightly. "They're kind of like monkeys without fur or tails, right? My friend Twilight sometimes goes through a mirror into another world where she turns into one."
Before any of the Rangers could question this, Gadget climbed into the Ranger Wing and keyed up the radio as the others followed suit. "Ranger Wing to Canine Squad; you read me, Flash?"
"Loud and clear, Gadget," the German shepherd's voice replied from the radio a moment later. "Everything okay?"
"Well, not exactly," the mouse told him. "Could you bring Doctor Drake by the Ranger Tree? We may have a patient for him to look at."
There was a brief pause, then another male voice came through the radio. "Sure I can come by; is Tammy busy, or...?"
Gadget handed the microphone to Tammy. "This one's a little beyond me, Al," she said. "How are you with birds and horses?"
"Fair enough, I suppose..." there was another brief pause. "Wait, birds and horses? I thought Gadget said a patient."
"Trust me," Tammy replied, "you'll see when you get here".
