Author's Notes:

Inspiration for chapter names:

https://www.youtube.com/watch?v=B6X26ZPGQV8

The ponies Twilight had cast the loyalty spell on were all in the castle, waiting for Luna to arrive so that Twilight could free Nightmare. "Okay, everypony," she said to the group. "I want you to ensure that nopony else gets into the castle, especially the other elements. Do I make myself clear?"

"Yes, Empress," the assembled ponies said at the same time.

Twilight nodded. "Good. Now, take your positions."

The group said what they always said when she gave the order, then went to their designated positions.

As soon as they had all left, she turned to Spike and said, "Send the letter, Spike."

"You got it, Twi," he said, saluting. He then brought up the letter that would be sent to Luna, and sent it her way.

. . .

Luna was enjoying a few minutes before Lunar court began, though she wouldn't be doing much, as many ponies went to her sister. She was reading a popular fiction novel when a letter appeared in the green flames that Spike had. She initially thought it was meant for Celestia, then remembered that it would work for anypony, so long as it was addressed to them.

She opened the letter, and read it.

Dear Princess Luna,
I've encountered a certain problem, and I was hoping you could help me with it. The reason I ask you for help is that it appears to be related to your kind of magic. If you are able, please come to my castle immediately.

Sincerely,
Twilight Sparkle

While Luna was surprised that Twilight had written to her, she was grateful, as it would mean she had something to do instead of just sitting around for hours doing nothing, and she was a little curious as to the magic Twilight had found.

"Guard," she said to the nearest Lunar guard, "how many ponies are scheduled for Lunar court tonight?"

The guard checked the scroll he had, and once he had the numbers, he looked to her and said, "None, your highness."

Luna smiled inwardly, as this meant she would be able to help Twilight with, and, if necessary, push Twilight away from this magic, as it was a dangerous magic that only the most powerful alicorns could wield.

She got up and told the guard, "Inform my sister that I will be in Ponyville for the next few hours. I wish to take care of something there, and I wish to handle it alone."

The guard bowed, saying, "Of course, Your Highness." The guard then got up and left the room, heading for Celestia's private chambers.

Now to see what Twilight Sparkle requires help with, she thought to herself.

She lit up her horn, and disappeared in a flash of dark blue light.

. . .

Luna appeared in Twilights castle with a flash of light, more specifically appearing in the largest library in the castle, when she had tried to teleport to the main hallway. She tried to move, but found she couldn't. She tried to teleport out of the room, but simply reappeared in the exact same location.

"What is going on?" Luna asked nopony in particular, which is why she was surprised when she got a response.

"Simple," Twilight said, walking to where Luna could see. "I'm righting an old wrong," she said, lighting her horn.

"What do you mean, Twilight Sparkle?" Luna asked, worried.

"Don't speak," Twilight said menacingly, "You aren't worthy of that. You never have been. Not since you became the prison of the true Princess of the night."

"What do you men?" Luna asked. "I am the princess of the night," she said in a snarl, "and if my sister finds out about this, she will banish you."

"And what," Twilight said, putting her face in Luna's, "makes you think I'm worried about that miserable excuse for a ruler? I could do much better. If she was actually a good ruler, I would have been more worried about death than banishment."

"What is making you say these things?"

"The truth," is all Twilight said before she cast a spell on Luna.

. . .

Twilight was a little surprised when the spells had worked, but was joyful, nonetheless.

As she and Luna were talking, she began to charge the personality spell. She placed her horn on Luna's forehead, and the resulting flash would have blinded if she hadn't cast a spell to prevent blindness from sudden light. Not that her eyes didn't hurt, though.

When she opens them, she still saw Luna, who also had her eyes closed. At first, Twilight had thought the spell hadn't worked.

Then she opened her eyes.

Instead of the teal blue, normal iris' Luna usually had, she now had the teal blue draconic eyes that only Nightmare Moon had.

She looked around, proving that this was Nightmare, and not Luna, as the spell had been designed to keep Luna, or anypony who thought themselves Luna, from moving.

"What am I doing here?!" Nightmare asked, using Lunas body as a mouth piece, "What is this place?"

Originally, Twilight had placed a second spell on Nightmare as the personality spell was cast that would allow her to remember everything that had happened. From Lunas perspective, that is, but it would take time for it to activate the memories.

"You're in my castle, Princess Nightmare. And you are here because I brought you back," Twilight said.

Nightmare glared at Twilight, saying, "I remember you. Tell me, why would Celestia's prized student bring back her mortal enemy?"

"Because," Twilight said, "you were unjustly imprisoned due to Celestia not paying enough attention to Luna, and thus not seeing her anguish. As such, you are in the right, and she is wrong."

"And what made you come to this conclusion?" Nightmare asked. "It was my understanding that all of the ponies believed that I unjustly attacked Celestia."

"That's because they haven't seen the events of that night. A few months ago, i drank a potion that made me see that night, and It was you who attacked first, yes, but it was Celestia who could have prevented it. She did not care for her sister, who was your prison, and it was because of her negligence to your beauty that ponies had forgotten the truth and believed that you were only a legend, an old mares tale," Twilight said, "and I wish to ensure she can't do it again."

Nightmare, though still wary, calmed down slightly, the memory spell taking affect. "So you bring me to your castle, or, rather, Luna, and keep me here, when your goal is acquired? That shows that you do have some intelligence in that head of yours."

"Actually," Twilight said, "the spell that prevented Luna from moving does not affect you. Though, I have lined the entire room with spells that prevent powerful magic from all but me."

Nightmare, not believing this, attempted to move her right fore hoof, and was surprised when she could. She then tried to teleport, only for her to reappear where she had been a few seconds earlier. She then tried an invisibility spell, which didn't work.

"The only powerful spell you can use," Twilight said, "is the spell Luna used that gave birth to your body." This drew an annoyed glare from Nightmare, but she tried it anyway. It worked, just like Twilight said it would.

"Much better," Nightmare said. "But I am still curious," she said. "Why? You are much more powerful than Celestia. Though I am glad to be in true existence once again, I wonder why you brought me back."

"Because I figured that you would want revenge for what she did to you, and I can help you with that," Twilight said.

"How sow?" Nightmare asked.

"Simple, really," Twilight said. "Over the years, Celestia has gained a few enemies, yourself included, and I'm certain thye would help us if we," she paused here, looking for the most innocent sounding word for torture, "persuade them with the right evidence."

"Oh, I am starting to like you, Twilight Sparkle," Nightmare said, flashing a grin, revealing her predator like teeth for a second.

"Please," Twilight said, holding up a hoof, "Call me Twilight."

"Of course, Twilight," Nightmare said. "Then you can just call me Nightmare."

"Okay, Nightmare," Twilight said, a small grin on her face. "I'd like to talk about who we could recruit, but that would be best to wait until the sun is up, when you have free time. We don't want you to act like yourself to make Celestia suspicious."

Nightmare chuckled a little, then said, "No, we do not. In that case, I shall return after the sun has risen. Until then, I suppose I shall have to pretend to be Luna, now won't I?

"Unfortunately," Twilight said, "yes. But once the plot to overthrow is in effect, that won't be needed, not in public. While you're here in my castle, you're free to appear as yourself."

"I believe I shall do that, Twilight. Until then," Nightmare said, using an illusion spell to change her appearance back to Luna, eyes and voice included. "Good bye." he made her way to the door, where she encountered those whom Twilight had cast the loyalty spell on. They all bowed as they saw her, Applejack and Fluttershy included. It would seem Twilight has already gotten some of Celestia's most loyal followers, she thought to herself as she stepped outside the castle. She lit her horn, and disappeared in a flash of light.