"How could a taco cause a dimension portal to go crazy?" Sunset demanded.
Twilight shrugged. "That's a good question, and I'm hoping we'll find an answer, but the fact that the cross-dimensional rip occurred when the magical feedback surge hit the taco seems significant."
Kim frowned. "Well, we were at Bueno Nacho. It's too freaky a coincidence."
Twlight nodded. "Don't ask how, but I think that taco acted as a...beacon, for lack of a better word, to guide the cross-dimensional rip. I'm just guessing, mind. We're dealing with a combination of an established dimensional conduit, improperly functioning dark magic, and electricity. In all my research, I've never encountered such a bizarre conflict of incompatible energies. It's going to take a while to calculate exactly what happened, and..." She looked at Kim and Ron sadly. "I'm afraid knowing how you wound up in Sunset Shimmer's world isn't going to help me get you back where you belong. That's going to take weeks of research into spells that have been sealed in Starswirl the Bearded's Aethenaeum for centuries."
"You mean I gotta be a donkey for that long?" Ron brayed.
"Well...you don't have to stay in Equestria the whole time," Sunset said. "Going from here to my Canterlot is easy enough—"
"Actually, I'd rather none of you return to Canterlot High for the time being," Twilight said. "Sunset Shimmer, I'm going to need your help to research the dimensional crossing spells. Kim, Ron, I'm going to need to run a series of tests to try to find some kind of link between you and your home dimension." She frowned at Sonata. "And as for you...I'd like to keep you under observation until I determine just how dangerous it is for you to be back in Equestria. Also, I want to find out if you're really willing to reform and not use your power for evil."
"Eh. I'm tired of being evil. Been there, done that," Sonata said. "I just wanna see what Equestria's like. I've been gone a really long time!"
Twilight smiled. "Alright then." She looked at Kim. "Are you willing to remain here while I try to find a way to send you home?"
"So not the drama!" Kim said. "Don't mind Ron's braying—"
"I can't help it! I'm a DONKEY!"
"—whatever it takes to get us home, that's what we'll do."
"Good. Sunset Shimmer? Can I count on you?"
Sunset tilted her head. "Of course you can, but...I guess...we're gonna have to go to Canterlot, aren't we?"
"Well, that is where the Aethenaeum is," Twilight said. She smiled gently. "It'll be okay...I promise. Trust me."
"One last thing," Twilight said. Her horn glowed; the whirring of the apparatus around the portal mirror quieted as the various arcane devices slowed to a stop. The sheets of magic funneling into the portal faded into nothingness, and the whirling portal vanished, becoming the smooth surface of an ordinary mirror once more. A magenta aura surrounded the book powering the portal, and it floated onto the table. "I can't risk leaving the portal open while I'm in Canterlot," Twilight said. "If someone accidentally discovered it...that could be a problem. Worse..." She gave Sonata an apologetic grimace. "I'm sorry, but I don't trust Adagio and Aria. If they somehow discovered the portal was open and came back to Equestria..."
Sonata sighed. "I know," she said. "It probably wouldn't be a good idea to let them come back, especially if it'd give them their powers back."
"Not until they can be supervised," Twilight amended gently. "Sunset Shimmer, did you leave your journal with one of the others?"
Sunset nodded. "I left it with Applejack. Want me to send a message?"
"Please do," Twilight said, passing the book over to Sunset. Sunset inked a quill and wrote a note in the journal.
Twilight nodded. Her horn began to glow, and in a bright flash, saddlebags appeared on her, Sunset, Kim, and Ron.
Kim looked at her saddlebags, which were beige and bore the same medallion mark on her flank. "Spankin'," she said.
Sunset floated the journal into her saddlebag. "So, are we taking the train to Canterlot?"
"Probably a good idea," Twilight said. "I need to introduce Sonata to my friends in Ponyville first. I'm leaving her with them while we're in Canterlot."
"Aww, I wanted to go on the train," Sonata complained.
"Sorry, Sonata...I don't think it's a good idea for you to be seen in Canterlot at the moment. Besides..." Twilight smiled. "I think you'll enjoy Ponyville."
"Alright...everypony follow me," Twilight said, headed for the library door. "We've got a lot to do, and the sooner we do it, the better."