Scientific discovery was a process that neither Cadence or Mayfly were familiar with, as was made obvious in the way they grilled Thorax on what had happened to him. When Twilight came in to land, they were asking him conflicting questions he couldn't answer, while at the same time giving him no time to actually answer.

"What were you thinking?"

"What were you feeling?"

"Do you thinking the act of dying triggered something to cause the transformation?"

"Did having Honeydew with you make any difference?"

"Would a chemical imbalance from being wounded have been a factor?"

"Did you feel a particular bond with Honeydew as you were..." Cadence was unable to finish asking that question, mostly because she found it strange to say, rather than hard.

Twilight gave Thorax a pitying look, then examined Mayfly's notes, for lack of a better word. They were more a eye-hurtingly nonsensical collection of scribbles, topped off by a cutesy picture of Thorax as a goofy little love bug.

"Would you recommend getting stabbed multiple times as an acceptable trigger for causing the transformation in others?"

"Mayfly!" Cadence gasped, "why are you so obsessed with him getting wounded as being part of his transformation?"

"Because it's the most unique factor in what happened."

"Except it isn't. If nearly dying caused this kind of transformation in changelings, I imaging there'd be a lot more like him running around. And I can't believe I'm saying that." Cadence quickly shook her head, "Since it's unique, I'm going to suggest that something else triggered it. Something that a changeling has never done before."

"Like getting stabbed as he saved sneaky ponies."

"Does she mean us?" Rocky quietly asked Bon Bon, getting a shrug back in answer.

"No, I mean like falling in love with a pony. Not an awful lot of changelings do that."

"So falling in love with a pony causes transformation?"

"Perhaps."

Mayfly pondered this for a moment, then looked Honeydew in the eye. "I love you."

Cadence groaned a sigh, "I think you have to say it to a pony you actually know and care about."

"But all the ponies I know are crazy. Except maybe Sunset. Sunset is nice."

Cadence sat up and smiled, "Alright, how do you feel about Sunset?"

"Sunset pony provides a good meal. Lots of love to share. This one never feels hungry around Sunset Shimmer."

"Okay," Cadence said slowly, feeling that she should've expected an answer like that from the changeling, "but other than as food, do you have other reasons to like her?"

"Umm..."

"Reasons to reciprocate the love she must feel towards you?"

Mayfly made a face at Cadence, "I'm not going to go so far as to say she loves me, or that I love her."

"Friendship is a form of love, isn't it, Twilight?"

"Huh?" Twilight said dumbly, not expecting to have been dragged into the conversation. Considering her encounter with her friends earlier, she wasn't sure she could answer it with even a semi straight face, let alone a happy one. "Sure, I guess?" Seeing as they haven't even asked how it went in Fillydelphia, she was also a bit miffed.

Her reply did at least get Mayfly to think, even if it got Cadence to look at her funny. "So you're saying that I've been feeding on her friendship love, and that it might've been intended for me the entire time? I haven't been feeding on her affections for others?"

"That's right," Cadence said with a smile. "Now, knowing that, how do you feel towards her? Do you feel you could give that love back to her?"

"What? No! I don't want to starve by giving my love to others!"

"That's not how love works. Love is infinite."

"If love is infinite, why are changelings almost always hungry?"

"Because you're using it wrong," said Thorax. "Ever since I became friends with ponies, I've never been hungry, and since you said that you've not been hungry since meeting this Sunset Shimmer, you're going through the same thing. Just give it a try. The worst that can happen is that nothing happens."

"Fine," Mayfly said begrudgingly, "but I don't expect this to-"

A pulse of magic lit up the area, forcing the ponies there to shield their eyes until it subsided. When they dared to look again, they saw that Mayfly had changed much like Thorax had. Her eyes were a soft lilac colour, and her carapace had filled out its holes, and had changed to a pale blue, except for a splash of amber over her belly.

"That was unexpected," Mayfly muttered, stunned by the sudden transformation. She walked around in a circle as she tried to look at herself, then stopped and went cross-eyed as she reached back between her rear legs. "I have a gender now."

"Really, please stop doing that," Trixie said as she averted her eyes from the changeling's rear end, right in front of her.

"I seem to be female. Why am I female?"

Cadence beamed at Mayfly, "This is amazing! All this time, the thing holding changelings back was your reluctance to share love with others!"

Twilight made a face of quiet contemplation as many of the others fussed around Mayfly. Back in the changeling hive, Queen Primus had said that the changelings had been left incomplete and broken. Was the simple act of loving another really the key to fixing that? Was that the simple method behind curing the biological plight of the changelings? Seemed preposterous to her, and yet the evidence was right in front of her.

"Hey, where are my antlers?" Mayfly asked, rubbing a hoof around her head and finding only a single unicorn like horn. "Why does Thorax get them, and not... me... uh-oh."

"Uh-oh?" Cadence repeated. "What does uh-oh mean?"

"Thorax is larger in stature, and has unique appendages capable of performing magic. Only queens have those properties. Thorax is like queen. That is bad."

"I'm not a queen," Thorax laughed nervously. It died as he saw the way Mayfly and some of the others were looking at him. "That's preposterous, I can't possibly be a queen. I'm the wrong gender for starters."

"Irrelevant," said Mayfly. "I'm not one to use language like this, but Queen Chrysalis is going to be pissed when she finds out. I mean, murderous rampage type pissed, and not just at you, because I too am a deviant of changelings now." Mayfly whipped around on the spot and pointed an accusing hoof at Cadence, "Why did you make me do this?!"

"Me? You're the one saying that Chrysalis is going to try and destroy you for being different!"

"I don't even want to be queen!" Thorax wailed.

"King," Honeydew corrected him.

"I don't want to be king either!"

All of them stopped as the sound of Twilight laughing reached them. "Really? Is freaking out about this wonderful thing the best we can do right now? I hate to break it to you, but Chrysalis is so far from important right now, that its laughable. It'd be a miracle if she even manages to find out about you. I think for now you should calm down, consider how this could help your people in the future, and remember that if Chrysalis does find out, you have some significant protection in the form of at least three alicorns."

Cadence nodded, "She could've said it better, but she's not wrong." She frowned as Mayfly and Thorax shared a look. "What?"

"Should we tell them?" Mayfly asked Thorax.

"Probably. Guys, I don't think you realise just how good Chrysalis is at gathering information. It's an essential part of the hive being successful. Under normal circumstances she'd probably find out by the end of the week. At the moment, I'll say it might take a bit longer, but she will find out."

"Then she's just going to have to accept you being under our protection," Twilight said with finality. "We aren't going to let her do anything to you."

"Let's see if you keep to that with entire changeling hive coming for you," said Mayfly. "There's also something flying towards us," she added, pointing a hoof to the east towards a dark dot in the sky that was gradually getting bigger.

"Should we hide?" Cadence asked, only to be ignored as Twilight used her magic to create a lens.

"That's a thestral," she said. "She looks panicked."

Shadow sat up sharply, her attention fully engaged. "What do you mean she's panicked?"

"I'm pretty sure there's only one thing I can mean by that," Twilight replied bluntly. "If you want elaboration, I don't think she's here to deliver good news."

It was a couple of minutes before the thestral got there, and she flopped onto the deck to catch a breath before attempting to speak. When she did, her eyes went wide as she say the array of individuals facing her. "Princesses! Thank goodness you're here! Is Princess Luna here too?"

"No, she isn't I'm afraid," said Cadence. "Is something wrong?"

"They found us!" the thestral squeaked. "They found Batsburg!"

"What?" Fleur squeaked in surprise, stepping forward. "Who did? When?"

"This morning. An army came to the foot of Foal Mountain, not far from the entrance to Nostralis." The thestral swallowed and looked both Cadence and Twilight in the eye for a split second before looking down. "Celestia was leading them."

"What?" Twilight said dumbly. "How could- What?"

"Princess Celestia is leading the army that's about to attack-"

"I know what you said!" Twilight's breath caught, ashamed at yelling at the distressed thestral like that. "I just don't believe it." Twilight glanced at Cadence, seeing the same disbelief.

"Please, we need help. We need your help."

Twilight... struggled. There was no other word for it. The very idea that Celestia would lead an attack on anypony was already beyond her comprehension, but to do it for Faust? There was no way she could be doing it of her own free will.

"Twilight!" Shadow yelled, snapping Twilight out of her stupor. "Fucking do something!"

"Uh, right! Fleur, get on the speaker stone and tell Luna what's happening. Cadence, leave Flurry with Shining and come with me. You too Ember."

"What?" both Cadence and Shining shouted.

"Shining can't fly, and I'm not facing Celestia on my own, so Cadence, you need to come with me!"

"But Shining's the fighter, not me!"

"He's also just a unicorn!"

Shining gave Twilight a look, "So?"

"So you're not going!"

Shining shook his head at Twilight, not bothering to actually spend time arguing with her. Taking Flurry in his hooves, he gave her to Thorax. "Do you mind?"

"No, of course not," Thorax took Flurry in his own hooves, "just go help the thestrals."

Shining kissed Flurry on the forehead, then stepped aside to let Cadence do the same. "I'm coming."

Twilight blinked and shook her head, "Apparently you are. Trixie, you're coming as well."

"I knew I should've stayed at the retreat," Trixie grumbled, not really meaning it. Much.

"What should we do?" the filly asked.

"You... stay safe." Twilight smiled sadly as the filly huffed, "I think fighting Celestia is a bit beyond anypony without serious magic. Sorry."

The filly waved a hoof dismissively, "It's fine, just go. Didn't feel like getting killed today anyway."

Twilight smiled at the filly, and grabbed Trixie as Cadence picked Shining up in her magic. Ember took off after them, and Shadow as well.

"Shadow, I don't-"

"Don't you even dare finish that sentence," Shadow warned. "I am not sitting here while my people need me. At the very least I can help with the evacuation."

"Alright," said Twilight. While Shadow's injury was a concern, she was actually going to say that she didn't know where she was going. At least Shadow gave her a way out of that now. "Lead the way."

A massive golden shield covered much of the area between Hollow Shades and Nostralis, and ended on the ledge by the entrance into the thestral city. If they wanted a sign that Celestia really was there, they'd got it, and then some.

It was also serving a tactical consideration beyond protecting the Mareitanians beneath it. It was also protecting the ponies scaling the side of the mountain, attaching ladders to the rock to give the attackers an easier method of getting into the city.

Other than that though, it was very hard to tell what was lurking beneath the tree canopy. There could've been several thousand soldiers down there. At the very least the trees were preventing the use of siege engines, although they probably wouldn't have been much use against the mountain anyway.

"This is bad," Shadow said as they skimmed over the shield to the entrance. "We never even considered Celestia. She's one of the few ponies that knows Nostralis even exists, let alone where it is, and how to get in."

"It won't be long until they're ready to attack," Twilight surmised. "I'd give it half an hour, tops." Twilight placed Trixie down on the ledge and landed, and only then did she notice that there wasn't a thestral to be seen. "Where is everypony?"

"I don't know," said the thestral that came to warn them, a small, mousey brown thestral that had been identified as Mouse, pun probably intended. "Greywhisker said they were going to start the evacuation, and they couldn't have gotten everyone out yet."

Shadow stared stoically out over the shield, although it was easy to see the worry in her stance. "Something must've gone wrong."

"And I think I know what," said Trixie. Her horn lit up, and there was a crack from the mountainside above them as she pulled a chain net free from a crevice. "Apparently the Mareitanians are exporting their ideas here."

"Why haven't they fired on us yet?" Twilight wondered out loud. She supposed they couldn't get the angle right over the shield to fire right at the entrance where they were, but they could see the entrance well enough to get their shots mostly right for those flying out of it.

"I'm calling it here," Shadow growled, "the Mareitanians fucking suck."

"Aren't there any other ways out of the mountain?" Shining asked.

"Nope. Always thought that was a bit stupid. Now I know it is." Shadow gestured with her head towards the entrance, "We should probably go in and see what the situation is."

Trixie laughed humourlessly, "I'm going to out on a limb here and say it's not good."

"We'll see," said Twilight, thoroughly agreeing.

They let Shadow and Mouse lead the way in, and what they found was no surprise. Nostralis was in chaos as the few thousand trapped thestrals that lived here, with nowhere to go, panicked. It was at least a fairly polite panic that left the ground floor alone, where the Night Guard were gathered.

Shadow saluted once she'd reached the middle of the floor where Greywhisker was addressing the Night Guard, barely wobbling on her two legs left on the floor. "Captain."

Greywhisker looked up and breathed a sigh of relief, "Thank goodness. Good job, Mouse. Princesses, we are in dire straits right now, and could really use your help."

"Why aren't you trying to evacuate?" Twilight asked off the bat. "There can't be that many net launchers out there."

"At a guess, two dozen," Greywhisker told her. "If they stagger their shots while we're trying to leave, they could take out maybe a third of us as we fly out. Far more if Celestia comes and stops us."

"If she really wanted to stop you, she would've sealed the entrance to... this... shit." Twilight stomped a hoof in anger, "Celestia wanted you to get a warning out. She wanted us to come to your aid. I'm betting she's sealed the entrance now we're in here." Twilight groaned under her breath. Celestia was the pony that taught her tactical thinking. Why she didn't remember that earlier was an oversight she wouldn't forget very soon.

"Where's Princess Luna?" asked Greywhisker.

"She's probably on her way," said Cadence. "We were much closer, so we got here first. Captain, I appreciate that you've asked for our help, but without a plan to evacuate these ponies, I'm not sure what we can do. We can't hold off Celestia and an army."

"I realise that, but we have very few options. With those net launchers out there we risk losing a large number of thestrals."

"If you want to preserve your people, why not surrender?"

Greywhisker didn't answer straight away, which worried Cadence more than any stupid reason he could have given.
"Celestia made it very clear that she seeks to destroy every single one of us, calling us the abominable spawn of a monster, and that there shall be no mercy for us this time. Then she topped it off with a demonstration where she killed a thestral she'd captured using Solaris, turning her to ash."

"Sounds like a solid reason to panic to me," said Ember, to resounding agreement. "Still doesn't mean you shouldn't have a plan to get out of here."

"There's only one entrance," Greywhisker reiterated.

"Then make another!"

Greywhisker narrowed his eyes at Ember, "And who are you, dragon, to come here and-"

"Captain Greywhisker," Twilight said harshly, interrupting the thestral, "you will not insult the Dragon Lord, especially when she's come here to help you."

Greywhisker immediately backed off. "Apologies, Princess."

"Now, is there any weak points in the mountain that you think we can dig through?"

Greywhisker shook his head, "This place was built for safety. Everywhere is quite solid, I assure you."

"Built for safety," Trixie scoffed. "That's working well now, isn't it?"

"We never expected Celestia to betray us like this!"

"Stop, all of you," Shining commanded. "Bickering isn't going to get us anywhere." He pointed to the two lifts as they continued their journey in opposition to each other, "I'm guessing they're powered by water, yes?"

"By an underground river, yes," Greywhisker confirmed.

"Can you get out through that? Where does it come out?"

"It rejoins the Neighagra river, south of the mountain, but it's almost entirely underground. I can't say there's going to be many opportunities to breathe, and it would take at least five minutes to get through. I also can't tell you if it's got anything dangerous to go through."

"I thought the river was artificial," said Shadow. "How dangerous could it be?"

"If you can't breathe for five minutes, very."

"We can solve that," said Twilight. "Shining, do you think you could hold back the water long enough to get all the thestrals out?"

"That depends on how big the river is."

"Then I think we better find out. Greywhisker, how do we get to the river?"

Greywhisker sighed through his nose, but gave no other signs of disobeying. He walked back to near the lifts, and spent a moment searching around until he located a large square in the floor, the gap around it so full of dirt it was pretty much invisible. There were notches along the sides, presumably to place something to lever it out, but magic precluded that necessity.

Twilight lifted the slab out with ease, and placed it to the side, and inspected the slick, mossy steps in the hole. She lit her horn and cautiously walked down for the half a dozen meters, listening to the running of the river, and the rumble of the wheel driving the lifts, until it came to an open area. She brightened her horn until it was bright enough to see the entire opening.

"What do you think, Shining?" she asked. The river didn't appear to be that wide, at maybe six pony lengths, and around three deep, and the channel was very deliberately cut, and was likely so all the way through.

"There's going to be a lot of weight on that very quickly," said Shining. "I might have to have help."

Twilight nodded, irritated. Help meant Cadence, and Cadence could've been more use elsewhere. "Alright, Greywhisker, start organising your thestrals to get out of here, and Cadence, you help Shining. Trixie, Ember, we're going to be helping to keep the Mareitanians out, and I don't think we'll have long until they're trying to get in."

The evacuation had barely begun by the time the Mareitanians were ready to attack. Cadence and Shining were holding the water back, and the thestrals were flying out through the empty channel as quick as they could, but it simply wasn't wide enough to get them all through before the attack began. It also didn't help that the evacuation was taking place in the same area as the attack would come. Whoever designed Nostralis to be safe must've forgot their meds that week, in Twilight's opinion at least.

Twilight had situated herself in the tunnel leading to and from the underground city. Nearer to the outside, she could see a shining disc of golden magic, blocking their way out. It also confirmed her theory about Celestia wanting them there before attacking. Twilight was not looking forward to when Celestia came, for practical reasons, but mostly because she was Celestia. Twilight might've had her issues with the pale alicorn, but this was a considerable step too far.

"This is not how dragons fight," Ember muttered behind Twilight. "We roar, we smack each other around, we breathe some fire, and the loser slinks off. We certainly don't plan to butcher their entire family."

And perhaps that was the biggest sign that Celestia truly wasn't herself. She'd granted the thestrals clemency long ago, despite knowing they were created to serve her sister during her descent into becoming Nightmare Moon. If she could do that then, to now declare them abominations was very wrong, and to decree their wholesale slaughter was... well, it wasn't Celestia, in the slightest. It wasn't particularly Faust either. It was...

"It's an attack on Luna's children, not the thestrals." Twilight wanted to smack herself. Clearly her disappointment with her friends had left her a bit slow.

"Isn't that the same thing?" said Trixie.

"Yes, but also no. They aren't being attacked because of what they are, but because Luna made them, because she would come to protect them. Sure it would stop the Night Guard attacking elsewhere, but that's not what this is about. Not entirely."

Ember made a face, "You ponies are really messed up, you know that?"

"I'm starting to. I'm also wondering if we should try to warn Luna to stay away. Not that I really think we can at this point."

"I'll go," Trixie said eagerly.

"Not likely."

"Worth a try... oh boy." Trixie gulped as Celestia's shield vanished, marking what could only be the beginning on the attack. "Here we go."

"Are you sure you want me to do this?" Ember asked, sounding neither unsure, or confident.

"Now is really not a good time to be backing out," Twilight snapped impatiently, without meaning to. If Ember picked up on that, she didn't show it.

"I'm not backing out, but even you have to admit that burning to death is a really horrible way to die."

"I know, but if we really want to put them off coming down here, fear of a horrible, burning death is pretty solid way to do it. The fact that dragon fire is good at burning through shields is also a serious bonus." Twilight raised a shield, filling the passage as the Mareitanians started to creep in. "Get ready."

Blasts of magic sizzled down the tunnel, and impacted on Twilight's shield, doing very little to even scratch it, let alone break it. As far as Twilight could tell, they were doing it to distract her from seeing them slowly get closer, but it'd take more than a light show to do that. She could see them getting closer between the flashes, and when she felt they were close enough, she made a small hole in her shield.

Whoosh!

Ember breathed a torrent of flame through the hole, filling the passage beyond it with a vibrant purple flame that ate through whatever defences the Adepts attempted to raise. Twilight found herself having to reinforce her own shield as the blowback started to burn through it. Thankfully that provided a good distraction from the screams of the ponies getting burnt alive. Screams which lasted far too long.

"Always hated the idea of flame weapons," Trixie said, shuddering at the thought of being at the wrong end of what Ember was doing. "No offense."

"None taken," Ember said back as she banged a claw on her chest and coughed. "Not sure I have more than a couple of those in me."

"That's fine," Twilight told Ember. She recoiled as the stink of charred flesh hit her nose, and she really, really hoped those ponies were dead.

Everything went quiet for a moment after that, except for the plink plink of the stone passage as it cooled from Ember's flame. Twilight instructed Trixie to go and see how the evacuation was going as they waited for what came next. They weren't to be disappointed.

"They're not even halfway thro-" Trixie stopped running towards Twilight and Ember, turned around, and slinked back the way she came as Celestia entered the passage. Celestia didn't even look at the bodies as she walked down, and didn't show the slightest sign that the smell bothered her, even though it had to have been.

Twilight felt horribly conflicted about it, but she opened another gap in the shield for Ember to breathe more fire through. The heat was intense as the flame became trapped between two shields, and it occurred to Twilight that Celestia was more likely to outlast her in this situation, so told Ember to stop.

Ember burped unhappily, and held a claw over her mouth, and another over her stomach. "I think I need to be a lot bigger to sustain flames like that. I'm done."

Twilight nodded and waved her down the passage. Her attention was on Celestia, who was none the worse for Ember's efforts. She was currently waiting for the area to cool again, giving Twilight a chance to really look at her.

Celestia's mane and tail had been done up in a plait that kept it out of the way, and free of her armour, which was done in an ivory colour, except for the golden trim. Solaris was held by her side, the spear burning with a heat that made Ember's breath look like a campfire in comparison. What Twilight mostly saw were her eyes in her stern expression visible through her helmet. Well, that, and how much taller than her Celestia really was, but mostly the eyes. They were cold, hard, and seemed to settle on a look that sat between anger, disappointment, and disgust. It was like looking into the eyes of an entirely different pony.

"Hello Twilight," said Celestia, in what was otherwise a pleasant, conversational tone. "I'm going to give you one chance to leave. You already know this isn't about you, and I'd rather not harm my former student, even you are betraying me further by being here, helping these creatures."

"So you suddenly hate thestrals now, is that it?"

"No, I don't hate the thestrals, but they are an unnatural creation that have no place in the world my Mother is creating."

The mechanical delivery of the words ground on Twilight's nerves, but she did her best to ignore it. "That's bullshit. You're attacking the thestrals to draw Luna out. You don't care about their origins, and you never did!"

A sad smile curved the corner of Celestia's mouth, "That was true, once, but the fact is that the thestrals will never accept their place in the new order of things, and so they must be removed. Mother has entrusted me with doing so, and I will stop anyone that attempts to impede my duty."

"Entrusted you? Tell me, Celestia, has she entrusted you with raising the sun yet? Or does she not trust you enough for that?"

"Don't try and bandy words with me, Twilight. Mother will allow me to resume my duty of raising the sun when the time is right. I am content to wait."

"Why are you talking like Luna?" Twilight asked, hearing the same slightly archaic speech patterns coming from Celestia that Luna used. That wasn't the question to be asking, apparently, as Celestia slammed the point of Solaris against Twilight's shield with a snarl. A sharp pulse of magic through the crack she made shattered the shield, and Twilight teleported away back down the passage, placing another shield in the way.

"Incoming!" Twilight shouted, although the Night Guard were already in position to fight, as was Trixie, which Twilight was more than appreciative for. "Greywhisker! Get those ponies moving!"

The thestrals started pouring down into their emergency exit as fast as they could, quite often blocking each others' way. It really wasn't any faster, and as Celestia reached Twilight's shield, Twilight found herself wishing to be anywhere but where she was. She was about to witness the murder of civilians. Ponies who were utterly helpless against an alicorn. If this didn't replace the pegasus massacre at Prance in her nightmares, she guessed nothing would.

A pained whine escaped Twilight's throat as Celestia used Solaris to brute force her way through the shield, and no matter how much power Twilight put into it, it was like trying to hold back the sea. Twilight hoped that Faust had given Celestia a boost somehow, because the idea of this being Celestia unleashing her full strength, a strength she'd kept hidden, didn't sit right in Twilight's head.

The shield buckled, and Celestia strode into Nostralis. The Night Guard swooped in to attack her as the Mareitanian soldiers poured in behind the alicorn. Twilight wanted to scream at them to stay away from Celestia, but her voice was lost to her at that moment, and all she could do was watch in horror as Solaris was swept around in a wide arc, slicing through two of the thestrals, and reducing them to ash.

Out of the corner of her eye, Twilight saw Trixie backing away as she shook her head and swore repeatedly. She then turned and ran for the escape, pushing her way down in with the thestrals. Twilight didn't say a word as she did. There was nothing she thought she could say, but there was plenty she could do.

Twilight's horn burst into action with a blaze of energy that she directed at Celestia. The Night Guard could keep the soldiers distracted enough, but she knew that only herself was enough to stop Celestia carrying out her grim duty, so she rained destruction upon the once noble alicorn, forcing her onto the defensive.

Celestia took to the air, a move which Twilight calculated to mean she didn't want Twilight's stray magic to harm her soldiers, while also giving Celestia the chance to fire at the thestrals. Twilight didn't want to give her the chance, so launched into a barrage of magic that Celestia had to shield herself from. Twilight knew that the longer she kept Celestia shielded, the less she could do.

A blast of searing magic flew past Twilight, singeing her feathers and making her skin prickle with heat. Screams from below informed her that the thestrals had been hit. Twilight saw her mistake straight away after that. Solaris was still outside the shield, and could attack with impunity, while Celestia was safely within her protection.

Another bolt of magic from Solaris soared towards Twilight, and this time she intercepted it, catching it on a shield before it could harm others. She only just blocked it though. The sheer power behind it was more than Twilight would expect. She had to keep Celestia from firing more, because there was no way she could block every single spell.

Twilight flew up, trying to get a better angle on Celestia, who was watching her as she went up, but didn't move to match Twilight's elevation. That suited Twilight just fine as she pulled up into a loop that had her facing back down towards Celestia. A thin, yet powerful beam of magic erupted from Twilight's horn, running over the surface of Celestia's shield and cracking it enough that when Twilight reached the bubble, a hard kick from her was enough to shatter it.

Twilight darted away as Celestia swung her weapon towards her, and summoned her blade Swordy to block the return swing. The blades locked together, and as a struggle of power and will began, Twilight hoped Swordy was up to the task. The heat pouring from Solaris would've been enough to make any normal sword soft in seconds.

"You know neither of us wants this," Celestia said as the struggle continued. "We're fairly evenly matched. I have millennia of experience and practice, and while you have skill and raw power, I'm the one that taught you magic. I know things you don't."

"Oh yeah?" Twilight hissed. She feel the skin on her face and front beginning to blister from the heat. "You also have something else I don't."

"And what might that be?"

Twilight shoved the two weapons to the side, and swung her rear around and did a little twist that she knew she couldn't have done if she was really thinking about it. It did get her into the right position to bring her back right hoof around in a hard kick on the side of Celestia's head that made her helmet ring.

"That's what!"

Celestia growled and backed off, pulling her now dented helm off and casting it aside. "I suppose I shouldn't be surprised that your obsession with winning would make you fight dirty."

"You've only yourself to blame for that one," Twilight spat back at Celestia. "I learnt a lot in Mareitania, and fighting dirty is only part of it."

"Is that so? Then I hate to inform you that two can play at that game." Celestia turned in mid-air, bringing Solaris around as it blazed with the build-up of a spell that made Twilight's eyes water. A beam of superheated energy lanced from the spear in a stroke that swept through the still escaping thestrals, killing over a dozen of them in seconds.

Twilight screamed with rage and launched herself at Celestia, a pulse of magic sending the white alicorn flying away onto one of the ledges surrounding the outside of the city. Twilight flew after her, her eyes glowing bright white as her rage and desperation triggered that place deep inside her that refused to give in to anything.

Celestia shielded herself from another blast that smashed the rock around her, sending her tumbling to the ledge below. She fired her magic at Twilight, but the smaller alicorn batted it away as she came after Celestia again, and focussed her magic on crushing the life out of her former mentor. Celestia cried in pain as black started to creep in around the edges of her vision, and then cried louder as her own survival instincts kicked in.

Twilight jolted as Celestia returned her attack with a shockwave that shattered the ledge she was on, the ripple it caused collapsing the entire level around the city. She teleported as a more direct attack was fired at her that cut scores out of the other levels. Twilight counterattacked with a beam of magic that Celestia met with one of her own, and another battle of wills began, but this one of magic instead of weapons.

Through the haze, Twilight became dimly aware that what she was doing wasn't working. She was also becoming aware that the roiling mass of magic between herself and Celestia wasn't dissipating. It was building. Celestia wasn't fighting her magic, she was absorbing it, adding it to her own in what Twilight could only describe as a magical bomb that would devastate Nostralis, and pretty much kill everything in it.

Twilight snapped back to reality and teleported up in a move that Celestia hadn't predicted, and the force of her own magic slammed the bomb into the wall without Twilight's to counteract it. A wave of destruction, far less than it could've been, flew out from the impact, forcing Celestia to shield herself.

Twilight gawped in shock. The fact that Celestia had the awareness to do that during her 'panic mode' was astounding, and proof that Celestia really did know things that she didn't. But that didn't answer all her questions though, such as how Celestia was able to even consider doing what she had just attempted. She was going to kill everypony in the cavern. Celestia, the pony that Twilight had long considered a paragon of all that was good, even if that good only fully existed in those history books written by the victors. Even at her worst, she couldn't have done something like what she just attempted to. She would've killed her own soldiers as well.

"Do you even realise you could've just done? Do you even see what Faust has made you into?"

Celestia didn't answer. Celestia didn't need to as she prepared to attack once more. Apparently she'd passed the point where she cared about what Twilight had to say. Twilight nodded, accepting that words really were useless now, and she flew into action.

A dance of spells and shields began between the two alicorns, neither of them able to best the other, no matter what they tried. There was no angle they could find, no spell they could use, or defence that they couldn't utilise to best their opponent. They were at a stalemate, fighting now to outlast the other before exhaustion set in.

"This is pointless, Celestia," Twilight shouted, a small shield forming to block a single bolt of magic flying towards her. "The thestrals are almost gone, Luna isn't here, and you can't beat me. It's over. Just leave."

"No! My Mother has entrusted me with this, and I will not disappoint her! While you're busy with me, my soldiers will hunt those thestrals down until there are none left. There's nowhere for them to go down there, so it's only a matter of time."

"Uh... I'm not really sure if that's a bluff or not. The thestrals aren't trapped down there. It's a river, it goes somewhere."

"What?"

"Didn't you know that?" Twilight smirked at Celestia's confusion, and glanced down to see what the situation on the ground was. The Night Guard were pretty much gone, but a silvery dome was protecting the remaining thestrals from the soldiers, meaning that Luna had to have made it since that was unmistakably her magic.

Twilight blasted Celestia as she also looked down, keeping her distracted from what was down there for a little longer. Celestia wasn't interested though, and recovered from the attack to dive for the shield to try and break through it. Twilight flew in and intercepted her, grappling Celestia and hitting her off course. A physical competition wasn't what Twilight wanted though, because that one Celestia would definitely win.

"Why do you keep fighting?" Celestia asked breathlessly, the impact having winded her. "What do you have to gain except your own destruction?"

"Maybe I just enjoy pissing you off," Twilight replied, her voice hard. "Besides, I could ask you the same thing. You're quite famous for refusing to fight, up until now."

"I'm fighting to correct fifteen centuries of mistakes, Twilight Sparkle, and you're one of them."

"And what of me?"

Both of them looked up to see Luna hovering nearby, her face a picture of hurt and betrayal as her horn blazed with a build-up of magic.

"What am I to you now, sister?"

Celestia narrowed her eyes and sneered in disgust, "You aren't my sister, and you never were. You're nothing more than the unwanted spawn of a monster."

If Celestia's words hurt her more, Luna showed no sign of it. A moment later, both Celestia and Twilight were shocked as an impish smile crept onto Luna's face.

"So we all agree Faust is a monster then?"

Celestia's enraged shout was matched only by the boom of Luna's magic as she blasted the exhausted Celestia down onto one of the surviving levels. Luna flew after Celestia and pinned her down, stopping her from moving and casting magic, and forcing her to do the one thing Luna required of her. It forced her to listen.

"Today you have betrayed everything you ever cared about. Me, your student, your country, and even your very ideals. Worst of all, you murdered my children in cold blood. If you wanted proof of our shared heritage, look no further than our ability to make monumental errors of judgement!"

If Celestia had anything to say back, Luna didn't want to give her the chance to say it as she slammed Celestia's head down on the ground once, twice, and then three times. Celestia didn't move after that, save for a trickle of blood that escaped her nose, but Twilight knew she still lived, if barely.

Luna backed away, her limbs shaking. When she could finally bring herself to speak, her voice wavered with emotion. "Come Twilight, we need to leave."

"Luna-"

"Now!"

"Alright." Twilight flew down, and observed that the thestrals had mostly made it out, except for a few stragglers and what was left of the Night Guard. Both she and Luna reinforced the shield until they were through, then shrank it down behind them to cover over the exit.

"Is that all of them?" Shining enquired in a voice strained with effort, beads of sweat running down his brow. Twilight couldn't blame him for struggling. The weight of the water behind his and Cadence's shield had to be quite considerable by now.

"As many as is coming, yes," Luna said sadly. "You and Cadence need to go too," she added, taking over the shield.

"What about you?" asked Cadence.

"Twilight and I shall be along shortly, now go."

Both of them listened to the hoofbeats for a while as Cadence and Shining made their escape, but even that couldn't fill the gulf of silence that opened in their absence. Twilight wanted to fill it, but knew there was only one thing to fill it with, and she didn't know if Luna was ready for that. Twilight didn't think she was. Luckily, Luna filled the silence for her.

"What Starsy wants for Faust is far too good for her. In one day she has taken my sister from me, stripped her of compassion, and turned her on the ponies I love, my children." Luna raised a hoof to wipe her tears away, "There are no words that can adequately describe how I feel right now."

"I'm sorry, Luna."

Luna sighed at Twilight, "I'm sorry too. I'm not the only one affected by this, and I'm not the one that had to fight her as you did. You did well. Far better than could be expected of anypony in the position you were in."

"A couple of years ago, I couldn't have done that. I would've begged and pleaded with her to snap out of it, and if she attacked me, I don't think I could've fought back. The thestrals would've paid the price for that. Thankfully, Celestia herself has made it easier to fight back." Twilight glanced down the channel as the Mareitanians pounded on her shield, "Do you think they've had long enough?"

"It'll have to have been." Luna started backing up the channel, "Lower your shield and draw them in, then get ready to move."

Twilight obeyed, not about to argue with Luna at this point. She was going to put on a show that her shield was weakening, to make the Mareitanians think they were getting through, but at this point it was near enough to the truth that she didn't really need to bother.

The Mareitanians poured in through the gap, and Twilight snapped a few shots off as she ran to catch up with Luna, who was standing ready to run herself, joining Twilight as the smaller mare caught up. Twilight did her best to shield them from any stray attacks, while Luna maintained her barrier holding back the river for as long as she could.

Soon though, Luna got too far away to effectively maintain the shield, and her horn started to flicker with the strain. At that point she gave up trying, and spread her wings to fly as the river reclaimed its course, no matter who happened to be standing in it.

The roar of the water, and shouts of the ponies swept up in it filled the tunnel, and both Twilight and Luna took flight, going as fast as they could through the narrow pathway. The pressure of the air being pushed in front of the river helped propel them along, but as the spot of daylight in the distance grew larger, the river was nipping at their heels.

Both of them pulled up as soon as they were able, letting the river explode out of the tunnel behind them, and carry its grim cargo of bodies to the Neighagra river. The bank nearby was lined with thestrals, and those few that came to help them, including Rainbow and Lightning. All of them seemed shocked by what had happened, and more than a few were shedding tears. Luna landed amongst them, while Twilight headed for Ember, who was standing next to Trixie, whom Twilight didn't particularly wish to address right now.

"Are you hurt, Ember?"

The dragoness turned on the spot, pointing out a few lines cut into her scales using claws stained red with blood. "It's going to be ages before these all grow out. Apart from that, and a stomach ache, I'm fine."

"Good."

"What happened to Celestia?"

"She's been taken care of for now. We'll be well away from here before she comes to." Twilight saw Trixie turn enough to look at her out of the corner of her eye, but failed to meet Twilight's gaze when she looked back. "Have something to say, Trixie?"

"Other than to say I'm sorry, no, not really."

"Oh good, so you are sorry."

"Twilight, she turned ponies into ash! Not just any ponies either, but thestrals wearing armour! I'm sorry, but Trixie is still far too attached to her mortal coil to risk something like that. Besides, what chance would I stand against a pony like Celestia?"

"You've fought me before."

"Yeah, and I lost, and then you told me you were holding back to avoid killing me. If Celestia saw me using dark magic, I really don't think she'd have been as merciful as you."

"Alright, fine, so you don't fight anything that stands an actual chance of killing you. I'll try to remember that."

"You don't have to say it like that!" Trixie turned to fully face Twilight, but kept her next words to herself as she saw the tiredness in Twilight's stance, and the faraway look in her eyes. "Are you alright?"

Twilight barked a bitter laugh, "That question. Trixie, I just had to fight a pony that was like a second mother to me for years, and watch her kill innocents in an act that went against everything Celestia used to be. No, no I am not alright, but I think Luna's got to be feeling a lot worse than me."

"I guess." Trixie shrugged helplessly, "So what do we do now?"

"Now?" Twilight sighed explosively, conveying that she didn't really know. "I suppose we need to find somewhere to house a couple thousand thestrals. I dread to think of what's happened to those thestrals that didn't live here."

"Is it worth doing something about that, if we can?"

"Is it worth it, yes, but not necessarily possible."

"Oh. I guess all we can do is hope they got themselves to safety in time."

Twilight nodded, as that really was the most they could hope for. Perhaps they might be able to figure something out if they learn those thestrals were taken captive, but judging from today, catching them seemed to be the last thing on Faust's mind.

Twilight was interrupted from her musings as Cadence came over and pulled her into an embrace. Twilight's initial instinct was to push her off, but didn't. Instead she sank into it, breathing softly through the small bit of comfort it gave her.

"You're so brave to be able to face Celestia like that," said Cadence. "I don't think I could've done that. In fact, I know I couldn't."

"You'll be surprised what you can do when you have no choice," Twilight said back. "I doubt this will be the last time we have to do this though. If we want to get to Faust, we now have to go through Celestia."

Cadence nodded, then rested her head on top of Twilight's for a second before releasing her. "Luna's trying to hide it, but I can see how much this has effected her. If the thestrals weren't here to distract her, we'd probably be trying to talk her out of going after Faust."

"I don't think that's a mistake Luna would make twice. She knows Faust would wipe the floor with her again."

"And I am not so deaf as you would believe," Luna said as she walked over to them. "Faust will indeed pay for this, and premature action would only foil that."

"Oh Luna-"

Luna held up a hoof to stop Cadence as the pink mare moved to hug her too. "I am far from in the mood for such things. Right now I need to think of where to keep the thestrals safe."

"The only place I can think of," said Twilight, "that Faust wouldn't dare go, is Griffonia. Maybe the Circen desert, but I don't think that's really the place for thestrals."

"I suspect you are right," Luna said sullenly. "Let us hope that dear Hergest's patience with us can be stretched a little further. Let us get moving before we are discovered, and hope nothing goes particularly wrong."

"I'll have to catch up to you. If you take Trixie, I'll go with Cadence to take Shining and Shadow back to the boat, fill them in there, then come back with Cadence, Flurry, and Mayfly."

"Very well, but I shall request you do not dally. With Celestia now fighting for Faust, I feel that the noose around our necks has become a little tighter."

Fleur, and all of them, were speechless as Twilight described what happened in Nostralis. To think that Celestia could turn on Twilight and her sister like that and do what she did to the thestrals, they could scarcely believe it. The weariness in Twilight's voice only made it more believable.

"I hope you realise how dangerous it is for you now," Twilight said meaningfully. "If Faust orders Celestia to hunt you down, she'll do it, and won't stop until she has you. Personally, I'd feel better if you gave this up entirely, and came back with us."

"We can't do that," said Shining. "The less distracted Faust is by us, the more focussed she is on you. You've already lost one distraction today, so we're going to have to work that much harder to make up for it."

"Does that mean we're still going after the Shades?" asked Bon Bon.

Shining looked to Fleur for confirmation, and got it in the form of a small nod. "It does, except we're going to do it with less cock-ups and running away. After today, we really need to step up our game."

"Don't forget to ask for help if you need it," said Twilight. "I can't guarantee we won't be busy, but you can still ask."

"That's comforting," said the filly. "Do you even know what you're going to be doing next?"

"I'm sure we'll find out soon enough." Twilight smiled sadly, "That also means we need to leave to learn what it is. Say your goodbyes, Cadence."

Twilight Velvet and Nightlight headed over to their daughter as Cadence took Shining and Flurry aside to make her own farewells. They embraced her from both sides, and this time Twilight found it hard to keep her tears to herself.

"It's okay sweetie, you don't have to hide it if you don't want to," Twilight Velvet whispered.

"This feels like a personal attack off Faust, like she thought of the one way to hurt us most, and found it in Celestia. I know that's probably not true, but it feels like it. The worst part is, with Celestia back, ponies are going to be so much more accepting of Faust's rule. If Celestia is on her side, why shouldn't they be?"

"I think most ponies are smart enough to know something's wrong with that," said Nightlight. "Once news gets out that she tried to use Celestia to exterminate the thestrals, no more proof will be needed of how unstable Faust is."

"I wish I could agree, but a lot of ponies don't have a favourable opinion of thestrals. Some might even be glad she tried to commit genocide on them." Twilight sighed as Nightlight squeezed her a little tighter, "Take care of yourselves out here. I don't know what I'd do if I lost you."

"You'd survive," Twilight Velvet told her. "You'd survive, because that's what you do. We're proud of you, for standing up to tyrants like Faust, and the Duke, even when it hurts to do so. I wish we'd seen this a little earlier."

"Don't sell yourselves short, you're standing up to Faust as well." Twilight broke the hug, and wiped her eyes, taking note that Shadow was being held by Fleur. She gave the unicorn a small nod, then turned to Cadence. "Are you ready to go?"

"No, but I don't think I ever will be." Cadence kissed Shining, holding it for several seconds, like it might be the last one they ever had. "Be careful, Shining. I love you."

Shining gave Cadence one last peck on the cheek, and did the same to Flurry. "And I love you both. Hopefully it won't be long until we can see each other again."

"Hopefully." Cadence heaved a sigh and pulled herself away from Shining. "Let's go, because if I stay any longer, I don't think I'll be able to leave."

"Alright. Come on Mayfly, you too. Bye everyone." Twilight took off, followed by Cadence and Mayfly. Fleur watched them go, still comforting the miserable Shadow, and once they were gone she leaned over to Shining.

"So how do you intend for us to try even harder?"

"By giving up our concerns over personal safety. If we really want to make a difference, we're really going to have to go for it, no holding back."

"And where do we start with that?"

"We start with the basics. Except for yourself, the filly, and Honeydew, all of us are going to have to learn to fight, and learn to kill. We can't afford anything less."

"Twilight!" Sunset ran over and hugged Twilight as soon as they walked into the observation area of the Retreat. "I'm so sorry Twilight, that must've been terrible, doing what you had to."

"It... wasn't the best," Twilight conceded. "At least we saved as many thestrals as we did. I take it Luna isn't back from Griffonia yet?"

"She isn't, and she said she might be a while." Sunset blinked as she took in the sight of Mayfly, "That's... new."

"Huh? Oh, yeah. Mayfly's reached an epiphany. Congratulations Sunset, you're her new best friend."

"I am? Neat." Sunset released Twilight, allowing her to head to by the window and flop over onto a cushion while Sunset talked to Mayfly.

"Please tell me there's some good news."

"There's some," Starsy said as he faded into view. "We've worked out a locking spell that should keep Faust contained, but... it requires some materials that can only be obtained in one place."

"And which corner of the world are you pointing us at now?"

"Zebrica, conveniently, since I understand that you'll be heading there at some point anyway. While time is an issue, I'm not saying that you need to go there now, because there's something else I'd like you to do first."

Twilight sighed and sat up, "And what's that?"

"If you're going to fight Faust, you're going to need protection. I do have some ideas on how to do that, which also stem from Zebrica, but I'd rather exhaust all our options first. Tell me Twilight, do you know where you can get a suit of rune warded armour?"

"I might," Twilight said slowly. "Adding to the conveniences, I have a suit in my castle. I'll get it tomorrow, because right now, I'm exhausted, and I want to think about what just happened."

"Any point about it in particular?"

"There most certainly is. If alicorns are immune to mind control, how did Faust get Celestia to do what she just did?"

Author's Notes:

You predicted Celestia. You were god damned right. Hope it was worth it.