Chapter-6: Investigation.
Twilight goes outside of the room and sees a curved, red horn. She takes it into the room to have a better look at it. She says to herself- “This looks familiar.”
Then, she hears a voice saying- “Long live the king.”
Twilight asks- “Who said that?”
The voice replies- “Don’t you recognize my voice, Twilight Sparkle? You are holding my horn in your hooves after all. Or are Alicorns unable to recognize voices?”
Twilight replies- “I don’t recognize your voice. And of course, Alicorns can recognize voices. Just tell me who you are.”
The voice says- “Patience is very important. Didn’t Celestia teach you that? You were her star pupil. And anyways, you’ll have to guess who I am.”
Twilight guesses- “Are you a changeling, whose horn somehow got cut off?”
The voice replies- “No. I never will be a changeling.”
Twilight gets impatient. She demands- “Just tell me who you are!”
The voice replies- “So, you couldn’t guess who I am. I am King Sombra.”
Twilight is shocked- “But the Crystal Heart destroyed you. You couldn’t have survived!”
Sombra says- “All that Amore’s weapon did was weaken my powers. I knew that it would destroy me, so I used a spell to put my shadow in my horn. So, the only thing that happened to me was the weakening of my magic.”
Twilight asks- “So, what will you do now?”
Sombra answers- “I’ll wait for my magic gets stronger, and then I'll take the Crystal Empire for myself. Who’s ruling it now? I heard the ruler of this Empire is just like Amore. I’ll be able to destroy her easily. They both were incompetent fools.”
Twilight gets angry. She half shouts- “Don’t you dare talk about Cadence like that!”
Sombra says calmly- “But if you do me this one favor, maybe I’ll spare the Crystal Empire from my tyranny.”
Twilight asks- “What favor?”
Sombra answers- “Take me out of here.”
Twilight says- “And let you destroy Equestria? No way.”
Sombra replies- “How do you know that I will destroy Equestria? I might even be reformed if you take me out of here. I’ll promise to be good.”
Twilight asks- “How do I know you won’t break that promise?”
Sombra replies- “We’ll make an unbreakable vow.”
Twilight asks- “How do we do that? I never found any books on unbreakable vows in any library.”
Sombra tells her- “I have a book on how to do it. You’ll find it on the third bookshelf. It’s called- A guide to unbreakable vows.”
Twilight gets the book.