Nopony says anything for a long time. The silence swells around Twilight's hooves until she knows they're waiting for her to justify her irrational behavior. "Look, I know it doesn't make sense, I just had to try, I just had to—"
Fluttershy takes a swift step up to her and takes her into a hug, and Twilight doesn't have the energy to resist. "I understand, Twilight," she says. "We all do. I promise."
Twilight looks into her eyes for a long second. She looks around the room at the ponies slowly nodding. In the opposite corner, Pinkie Pie is smiling the faintest smile Twilight thinks she's ever noticed. In a flash, she has a sudden vision of something impossible, and she knows if she can do it, she can do anything.
Fluttershy lets go after a few seconds, and Twilight walks over to Pinkie. Her mental floorboards start groaning and creaking, but it's too late to turn back. "Pinkie Pie?"
The pink pony's eyes meet hers, and neither has any idea what will happen next. "...Yes?" says Pinkie, tone impenetrable.
"I'm sorry for earlier. I'm glad you're here. Even a pony like me needs all the support she can get right now."
Pinkie's ears and face perk up, and she smiles that behemoth smile from when she introduced herself to Twilight the second time, and probably the first. "Twilight... There's nowhere I'd rather be than with you and with the rest of my friends! And I thought about what you said, and I realize that I can't see things the way you do without getting to know you better, or being you, which is impossible! I think." She puts a hoof to her chin. "Anyway, I figured something out that I wanna share with you."
"Yes?"
"Whether you're friends with somepony doesn't have to have a yes or no answer! It can just be kinda sorta, or itsy bitsy, or even teeny weeny! You don't have to be best buddies as soon as you meet! And I think maybe being not being super-duper close is sometimes the best way to be friends! Twilight, would you be my teeny weeny friend?"
Everypony is watching, including the side of Twilight that's collapsing for want of support, the side that's a sunless, starless sky. "...Okay," she says. It's the only answer. Twilight has figured something out, too.
Pinkie makes a fraction of a motion to hug her, but stops. "Woohoo! You won't regret it, I Pinkie-swear!" she yells in Twilight's face instead. "Now let's see what we can do about that big baddie!"
"Thanks, Pinkie, it means a lot," says Twilight. And she guesses it sort of does. "...Okay. You girls wanted to talk about Nightmare Moon? Let's talk about Nightmare Moon." She opens the ceiling hatch and lets in a trickle of the despair swirling above her head. "I... don't know what we can do, but here's what I do know. She is at least comparably strong to... Celestia. She can fly. She has the power to extinguish candles, teleport, fracture the ground, fire energy blasts, and control the moon. There's no way to know exactly how powerful she is yet, but there's no way it's not catastrophically. She's thousands of years old, and knows an unknown but probably huge number of arcane secrets and histories unknown to modern ponydom." Wood groaning, cracking under the weight of the flow. "And she's the bearer of... bearer of the... she has the Elements. I have no idea how she got free. I have no idea how she wrested control of the Elements from Celestia. I have no idea what her weaknesses are. I have no idea whether her stated motivations are true, because honestly, they don't make sense to me." Cold, dark water filling the hole she's digging. "I have no idea, really, what she wants from us, except our death. And I have no idea why she is even considered virtuous enough to wield the Elements at all."
A pause. "That, uh... sure is a thorough rundown," says Applejack.
"Darling, you make it sound so... hopeless," Rarity says, looking down.
"It... it is hopeless. I'm sorry, but I don't know what you want me to say."
"Say we'll do whatever we can," says Fluttershy.
"Say we'll do whatever it takes," corrects Rainbow Dash.
"Equestria has faced threats like this over and over for centuries," Applejack says. "It's gonna be rough, but I bet if the whole kingdom works together, we can take her down like a mad bull at a—"
"Girls, it doesn't work like that! We can't just decide to overthrow the strongest pony in Equestria, especially just by believing it! It's almost inconceivable that we could handle her even if she didn't steal the Elements. But she did. We haven't ever faced a threat like this! We've never been on the bad side of the Elements before! There is no known power in the kingdom that remotely rivals the Elements. Our enemy has them. Ergo, we've lost! It's over!" She's losing control over her inside voice and her heaving breaths.
Tinder has been idly staring at nothing in particular, but suddenly steps forward to her, and she sees his composure break for the first time since they met. "It's not over until we're dead, Twilight! This is real life, not chess! You don't get to resign! You're the most powerful mage for a hundred miles! We need you!"
Fluttershy capitalizes on Twilight's silence, and says, "Twilight... All over Equestria, there are foals being born. Tonight. Right now. They might never see the sun in their whole lives if ponies everywhere, ponies like us, don't do anything to stop her! It doesn't matter what happens to me, I can't sit here and do nothing. I'm more sure of it than I've ever been of anything." Her face is so blank and resolute as to be chiseled from granite.
Every part of Twilight's brain starts quivering, no pair resonating in sync.
She directs her gaze towards Rainbow Dash, who is grinning a sly expression like she just figured something out. "You're so smart, but you don't even realize that maybe she doesn't really have the Elements? Sometimes villains, y'know, lie? If you beat Celestia, you could just say you can use the elements, since only Celestia could do it anyway. It's not like Nightmare Moon showed 'em off."
A surprisingly savvy observation. But... "But wouldn't that lie collapse on her the first time she fails to produce the Elements in response to a threat?"
"...Huh. Maybe." Rainbow Dash tilts her head, then rights it again. "But maybe she thinks she's strong enough to make us believe she doesn't even need them, if she can kick everypony's rump without them. Like, she doesn't even have to use her full power to fight."
"That's... actually sort of believable. There's a chance it could be a ploy. But still..." Twilight says to the hooves her head is resting on.
"And if that's true... she's wrong. We have a shot."
"Like I said, I don't know what we could possibly do even if she's lying about the Elements. If even Celestia couldn't stop her..."
"Equestria has been good to us ponies for hundreds of years," says Rarity. "Dear, we've needed Princess Celestia for centuries. But this time, she needs us. To save the kingdom, and maybe to save her, too."
"But we don't even know she's still alive!" screams Twilight. "She spared Luna, but we don't know whether Luna..." Wait, what am I saying? "...No. No. You're right. That's not what matters. What matters is that we don't know she's dead."
Everypony's attention locks onto Spike as he burps out a piece of rolled parchment bearing the royal seal. Nopony says a word. Twilight grasps it in her magic and unrolls it into her trembling hooves.
"It says... You'll have to be smarter than a letter, Twilight Sparkle. That's it."
As Twilight begins to pace, cogs start turning. "Buck. Buck! She knows who I am. She knows I'm already trying to subvert her. She knows! Oh, buck, I probably just led her right to our door! I'm sure an Alicorn can intercept and trace a measly dragonfire letter! What was I thinking?!"
"Calm down, sugarcube," says Applejack. "Half the country's probably musterin' forces to strike back by now. I'm sure Nightmare Moon has better things to do than pay attention to us, since it's not like our group here knows what we're doin', to be honest."
"But I'm the Princess's protégé! How did I not realize it before? I'm a priority target!"
"Darling, I know you're an accomplished mage, but don't you think that's a bit presumptuous? Nightmare Moon didn't even seem to notice you in the crowd," offers Rarity.
"That's because she needs time to learn the state of things, what's happened since her banishment. I don't know how, but I suspect that's her top priority right now. She might raid the Canterlot library, or torture some of the royal guard, or, or... we have no idea what she's capable of, maybe she even knows divination!"
Tinder frowns at that. "There's no reason to jump to that conclusion... divination has been lost since before the Princesses ever appeared. There's barely any record of it at all. We can't let baseless fears stop us from fighting back."
"It's not a conclusion! I'm just trying to tell you that we have no idea what Luna's capable of! We don't know!"
"We don't have to know," he replies. "We just have to prepare for everything we can think of. If there's anypony I want on my side to do that, it's you, Twilight." His eyes start watering. "...Please. Maybe we can't win. But I know with your help we can push the odds."
Twilight is frantically trying on words and phrases in response, but she's not the next to speak.
"Twilight... please... I don't want everypony to die. I'm begging you. Help us."
She looks into the distant corner of the room at the pink pony sobbing as hard as anypony ever has. Something clicks shut in her brain, and something clicks open. Even as the darkness begins swirling back around her, she knows they're right. Everypony else is right. She's no alicorn, but she's powerful, and smart. Think about the problem for five minutes before you give up and claim it's impossible. You're just coming up with excuses to give up because you'd rather wallow in Celestia's death. But think about what she would want. You have to be... you have to be your own Celestia now.
Celestia didn't walk away.
"...Okay," she says. "You're right, all of you. I'll help you do... whatever it is we can. But I need some time to think. There are a lot of variables here, and there are a lot of very bad problems that are going to start arising very soon." Whatever she does next, she needs to be alone. The justification clicks into place: "Why don't you all go home and see your families? Tell them we're going to attempt a coup. I'll stay here and start thinking."
Everypony nods at this, as some of them wipe at their faces. They say their thanks, but Twilight has already begun brainstorming avenues of attack, methods of survival.
As they leave, she reflects a couple magenta bursts at her amulet, and makes a rough guess to the time. "It's about 6 AM. Let's meet back here at sunri—" starts Twilight, then stops.
"Twilight?" asks somepony.
She looks at them all, encircling her, her eyes wide and watering. She tries to pry open her mouth, but to no avail.
I have to see her again.