Prologue:
Once upon a time, there were two siblings. The sister created shimmering lights, making her the Princess of Light. The brother created relaxing shade, making him the Prince of Shadows. The created a balance, by adding their light and darkness to their sisters' day and night. The beautiful Northern Lights, and calming shadows under the tree, those were both creations of them.
Though they were opposites, they loved each other very much.
Then, five hundred years after their sister Luna's banishment occurred, the Princess of Light disappeared. To this day, nobody knows where she went.
Celestia sighed, and continued walking through the hallway. Luna was going to ask eventually, and she didn't want to tell her what had happened. Actually, even she didn't know. It was a mystery to all, even the immortal sun goddess, ruler of Equestria. Had she stopped at an incorrect time? Could they have found what they were looking for if they searched somewhere else? Or was it all a lost cause, and it was never to be seen again? Luna wasn't daft, she probably already noticed the absence. She just didn't know how to ask her sister, and it's not something asked daily, believe me.
Her thoughts were interrupted when a guard burst through the door.
"Your majesty!!" he exclaimed, "Word from the mines!!"
"The mines?" she asked, "What is it?"
"They've found something frozen, your highness," he continued, "And, according to their letter, you need to see this immediately."
"Letter? Let me see it," Celestia's magic grabbed the letter from the pegasus guard's bag, reading it as quickly as she could. "Inform my sister that we are to leave right away. Cancel anything we have scheduled for the rest of the day, tell them a grave matter of important has arisen, that requires my full attention."
"Yes, ma'am!!" the guard saluted, and ran out of the room.
"What happened, Luminosus?" she asked, when she was sure he was gone.
