Twilight sobbed quietly in the next room, Princess Luna's room, while the Princess waited patiently. Twilight was still overcome with grief over the state of her mentor, and it wasn't until several minutes of sobbing had passed that she was finally able to uncurl and look up at Princess Luna, whose expression was no longer hostile, but tired. Twilight stood, shakily, and looked to the Princess, “What happened?”
Princess Luna considered the question for a moment, then said softly, “The other Twilight Sparkle came to the gates, demanding an audience. One would have been given to her, only my sister had been entertaining the emissary of the Dragon Kingdoms, Lord Wycliff. When she was told to wait, I can only assume the other Twilight thought her plan for usurpation had been found out, for she launched a siege. Hundreds of mercenaries and exiles swarmed the palace, but by great good fortune the bulk of the Royal Guard was here already, training.” Princess Luna sighed and looked away, out the window, “Some six hundred highly trained guards lost their lives that day, almost three quarters of the Guard's strength, and seventy two of those were ripped apart by the other Twilight's magic. Spells we had sealed away shattered the ranks of the guards, drove them insane, or simply banished them to some place nopony was meant to know.”
Twilight gasped appropriately, “But... But where did she get the knowledge? Those spells are sealed for a reason, I only know of them because they're referenced in the books I've read, but there's never anything specific.”
Princess Luna snorted, “Initially we thought it had come from the Element of Magic, but she never once used it in the fight. I suspect she dealt with some malevolent force to gain her knowledge, possibly the same that abducted you and started this whole affair. Or maybe she just figured it out, she, like you, was very bright.”
Twilight found herself blushing for a moment, then shook her head, “No, cunning is more like, it's stupid to attack the palace, without a death wish anyway...” She trailed off thoughtfully, and Princess Luna nodded.
“Yes, perhaps this was some elaborate suicide, but I don't think so, not entirely. See, she made a bee-line straight for my sister, carving a bloody swath through anypony foolish enough to bar her path. She even cut down the Dragon Kingdom's emissary, a great lord of the Draconic people. Her magic was potent enough to carve him in twain, and she did so. Slowly. After killing Lord Wycliff, she continued into the throne room and did... Something to critically wound Celestia. I never saw myself, I was rounding up the mercenaries, pulling them into slumber and chaining them all together when I heard her scream. I caught the witch though, cackling over Celestia's body, drenched in dragon blood. Whatever she'd cast though had taken it out of her, she couldn't even defend herself against my sleep spell.”
Twilight paled at the destruction wrought by the creature that had worn her face, “But... Why? Why hurt Celestia? And, not to doubt but, why not kill her straight off after that much trouble?” She winced at Luna's glare, which softened thoughtfully after a moment.
“You don't think this was a lethal attack?”
“No, Princess, not after all the things she'd done. If she could rip Lord Wycliff in half, then... Then why not do the same to Celestia?” She gagged a little at the thought, and shivered at Princess Luna's expression, “I'm sorry, I must sound so... So heartless, but it just makes sense. Did she try to escape at all?”
Princess Luna frowned thoughtfully, “No, she didn't. Once she was captured she just sat in her cell and talked to herself, or just babbled like a mad thing, until the hanging.”
Twilight swallowed and had to sit down before asking, “What... What did she say?”
Princess Luna closed her eyes, her horn glowed for a moment, then a voice filled the room, “I die this day, but one day I will return,” The voice was Twilight's, but colder, more vicious, with the edges of madness poking through like razors beneath a cloth, “When I do, you shall all know of the power greater than any princess, and not even the rise and fall of a hundred dawns shall save you!” The magical recording ended with the sound of a gallows trapdoor, a cracking noise and a gasp from the crowd, followed by screams.
Twilight blinked, “What happened?”
Princess Luna gave the purple unicorn a steady look, “When the noose snapped her neck, she turned into a collection of sticks and silk, with a pumpkin for a head that, when it fell to the ground and shattered, sent forth a wave of spiders, panicking the crowd. Ponies trampled each other to escape, but others were bitten. The lucky ones got trampled, those spiders were unnatural.”
Twilight looked sick, and visibly gulped back gagging, “It's... She was horrible, she perverted what it means to be a unicorn, to wield magic, the essence of life... And she injured somepony with it, somepony that loved her and that wished her no harm at all...” Twilight shook herself with a shiver, then looked at Princess Luna seriously, “If she is part of a larger plot though, part of it looks like... Like she wanted me to have a hard time when I came back. If I came back. But if that was a part of her plan, why?” Twilight shook her head, puzzled now, her sadness suppressed for a moment by her curiosity, “I mean, I could reverse the damage just by being myself, I even have a way to heal Celestia, I think, so-”
“You what.” Princess Luna interrupted flatly, looking hard at the purple unicorn.
Twilight quailed under the Princess of the Moon's glare, “I... I found... Found a fruit that heals all wounds, and it seems... Seems to... Uh... Well I've used it before and... Um... I have it here, if you'd like,” She quickly brought the golden apple from the basket, noting with a slight frown that it was one of only three left.
Princess Luna took the apple from Twilight with her telekinetic grasp delicately, then began to magically scan the fruit, her power rippling across the surface of the metallic gold apple like moonlight over a disturbed pool of water. She frowned after a moment, “Strange, it doesn't seem magical, but there is an... Otherness to it, similar to whatever energy is around my sister's wound. How can I be sure this is genuine? It could, no offense, be a trick if you were indeed the Twilight that wounded her in the first place.”
Twilight winced but nodded, “You could test on an injured animal or pony I suppose. I only have three left though and it would be very difficult to get more. And I don't really know the limitations of the healing. I did see it heal a couple of ponies who had been impaled, and another that had been cut open by claws.” Princess Luna nodded, noting Twilight's discomfort.
“Okay.”
Twilight blinked, “Okay what?”
Princess Luna sighed, “Try your fruit.”
Twilight stared for a moment, then stammered, “Just... Just like that? But... What?”
Princess Luna shook her head, looking pained, “Believe me, we've tried everything else over the past three years, and... She only has a few more hours left at this rate. Not even the best magical minds could stop whatever it is that's eating at my sister, and after the other Twilight was hanged, she fell into a deep coma, her condition worsening from grief.”
Twilight blinked, “So the thing about her declaring a day of mourning for me and the two of you not getting along because of it was...”
“A complete fabrication, yes.” Twilight stared at the princess, dumbstruck, but Luna continued before she could interrupt, “I'll explain afterwards Twilight Sparkle, but for now...” Twilight nodded, and took back the fruit from Luna telekinetically while the Moon Princess fixed her with a fierce glare, “Heal my sister, if you can, for the love you say you bear her and for the sake of Equestria itself.”
Up close, Princess Celestia looked even worse. Twilight stood by her bed in a state of shock. Celestia had always been Twilight's mentor: strong, wise, vibrant and full of life. Here she was wasted, gray with pain and age, her body shuddering with every breath as if it were a death-rattle. Her legs moved fitfully, and her face twitched in an expression of pain, while the thin alicorn mare's once brilliant mane of hair had faded to a dull pink, lifeless and unmoving. For Twilight, this was more of a nightmare than anything the Librarian had put her through. He had tortured her, lit her on fire, burned books in front of her, locked her in a deep dark hole, and still Twilight felt more pain and anguish now looking at her mentor than she ever had before.
Twilight brought forward the silver bowl in which she'd crushed the golden apple, and delicately started feeding her mentor with gentle nudges of magic, tears running quietly down her cheeks as she did so, though the rhythm of feeding never faltered. It reminded her of the time she'd had a terrible fever as a filly, and her parents had been unable to come to the school. Princess Celestia herself had made sure that the young unicorn ate and drank enough to keep up her strength, only leaving to deal with matters of state or advance the sun and moon. In her delirium, Twilight had called her her other mother, which had made the brilliant princess smile sadly. Now, with their roles reversed, Twilight found herself taut with worry, and hoping beyond hope that this apple worked.
Princess Luna watched, outwardly impassive but writhing with worry inside. She wanted to believe in Twilight, and knew that this last ditch effort would either save the princess or condemn her, but it was either that or watch her sibling slowly waste away. She noted the care with which Twilight fed her mentor, the tenderness with which she eased each mouthful down the alicorn's throat, and found herself just the slightest bit jealous. She almost laughed aloud at the thought, but here she was next to Celestia's death-bed and she was getting jealous of the closest thing Celestia had ever had to a daughter. She was so amused and disgusted with herself that she was caught off-guard when the bandages started to glow around Celestia's chest as the magic of the apple took hold.
Twilight backed away hurriedly, hoping this was a good sign, though the apples had never done this with Scum or the others. She teleported back reflexively when the heart- and magic-monitors exploded, then watched as three points of light pushed through the bandages and fell onto the sheets. As soon as they pushed out, Celestia collapsed again, still comatose, but breathing stronger and with her mane and coat back to their usual shine. Twilight approached the bed cautiously, while medical ponies extinguished and removed the fried equipment, and looked at the objects that had been expelled from her beloved mentor. Three obsidian arrowheads lay on the bed sheet, each one engraved with impossibly complex swirls and patterns. A whisper from the shadows told her what they were, and she immediately collected them in the silver bowl, careful to use magic and never touch the objects directly.
Princess Luna was overjoyed at her sister's recovery, despite her lack of consciousness, for Twilight's strange fruit had managed what three years of constant medical care had been unable to accomplish. She was about to congratulate the unicorn when she noticed her collecting the arrowheads carefully, “What are those, Twilight?”
Twilight was staring at the arrowheads, frowning, “Dream-poison,” she said absently, “A kind of psychic attack contained in a physical object. It's passed on by being in contact for extended periods, and can cause all kinds of damage. The... Things that took me use it sometimes, I've read, and there's no conventional cure for it.”
Luna frowned as well, staring at her sister, who was still making little pitiful noises, her legs kicking gently as she fought whatever nightmare tormented her. “So, she's stuck like this then? In a nightmare? Forever?”
“I didn't say that, Princess.” Twilight straightened and faced the Princess of the Moon, who was struck by how much taller the unicorn had become, she was almost at eye level to the midnight alicorn, and Twilight's eyes seemed to glow with determination, “I can enter her dreams, Princess, and free her.”