It was midnight.

Beneath a backdrop of shining stars, the waning moon hung high in the sky casting its cool evening glow amidst the shingled roofs of Canterlot. The sounds of the night were soft and gentle with only a light breeze whistling as it meandered through the narrow streets and alleyways. The looming towers of the castle ascending high into the skies cast only a faint shadow over the town, perched like guardians over its citizens. Inside the castle, the halls were dark and silent as the ponies inside slept soundly.

Princess Luna lay in her bed, a faint ray of moonlight shining through the window and onto her body as she slept. Like every night, she was fulfilling her duty of rising the moon into the sky and monitoring the dreams of ponies asleep throughout the kingdom. Curled comfortably beneath a multitude of blankets, the princess of the night stirred as her subconscious came upon a soon-to-be nightmare of a young filly sleeping somewhere in the kingdom.

"Help! Somepony help me!"

A young filly plead out in the darkness, surrounded by a sea of trees beneath sinister skies. In the darkness from all around her were unrecognizable shapes with menacing eyes piercing through the fog around her. Her mind began to race as no one came to her rescue, and the monsters surrounding her began to slowly creep towards her from every direction. She plead out again, but once again there was no help to be found. As the undefined figures closed in, she felt her vision go darker as the hope for rescue dwindled and she submitted to the darkness.

But in a flash of light from the skies, the moon pierced through the clouds, illuminating the forest and dissipating the fog to reveal the creatures that were closing in upon her. The young filly still cowered on the cold forest floor with her eyes closed tightly, but the tender embrace of Princess Luna brought her back to her senses. She first looked up at Luna, whose gaze made her feel exactly what she needed in this particular moment: a loyal protector she could call a friend. Her eyes then looked around her where the sinister creatures stood only moments prior, and she realized that they were a myriad of misshapen rocks and trees and bushes.

She looked back to Luna and cried softly.

Luna embraced her tightly for a few moments. "You mustn't be afraid, young one. Remember that you are in control of your own dreams, and that nightmares are merely representations of the strife we are currently feeling. The monsters are only as real as you will them to be." The young filly tried to fully grasp the meaning behind the words, but the love and tenderness behind them was really what helped.

She thanked her and let out a few more sniffles. The surrounding forest of her dreamscape slowly came to life as her thoughts became clear and confident. The wind moved softly through the treetops, rustling the leaves above them as they stood on the forest floor. The young filly closed her eyes briefly, her mind lost in thought. Luna took only a few moments to enjoy the peace she had fostered, but soon thereafter let her subconscious drift away to another dreamscape. There was always somepony somewhere who needed her assistance, and every moment she let pass in a dream was another moment a nightmare would continue to persist. Like the wind rustling through the leaves, her presence drifted away with hardly a trace.

The young filly now stood alone once more amidst the sea of trees, wondering where Luna went. A pang of loneliness resurfaced in her subconscious, which manifested itself as a bolt of lightning from the darkened skies above.

"Where did you go?" She plead, taking to her hooves and running through the trees to go after her only friend. A fire had erupted from the bolt of lightning and quickly began to spread. The young filly continued to run through the trees, searching for Luna. But she was long gone. The sinister shapes returned, this time appearing in the flames that licked against the forest floor. In the last moments before the flames closed upon her, the young filly looked up to the skies and saw her reflection in the moon.

It was Princess Luna.

"Sister, are you okay?" Princess Celestia burst through her bedroom doors and rushed to Luna's side. "I heard a scream."

Luna lay silently for a few moments, trying to process what had just happened before speaking. "I had a nightmare..."

Celestia frowned. Seeing her sister like this tore away at her heart. "Is it the Tantabus again?"

Luna wondered for a moment. She thought that she had worked through the issues that led to the growing Tantabus inside her, but perhaps something new was eating away at her that she was unaware of. "I don't think so," she replied, unsure of herself. "I've never had a nightmare like this. Usually it's me in the dream, but this time...I had taken the perspective of a young filly I thought I was protecting."

Celestia frowned again with a growing look of worry. "You...saw yourself in your own dream?"

"Yes."

"If that is so, then that would mean the ponies of Equestria went without your protection this night."

"It would."

The air was silent for several moments before Celestia did her best to reassure her, but there was only so much she could do. Celestia left the room shortly thereafter, worrying greatly about her sister. Luna returned to her slumber, hoping that she could return to protecting her citizens' dreams as she always did, but lingering doubts kept resurfacing in her mind as she drifted slowly off to sleep. Something was deeply, deeply wrong, and she would need help to fix it.

The next morning, Celestia sent out two letters detailing an urgent request for help with Luna's predicament. One to Twilight Sparkle and the other to Starlight Glimmer, who arrived in the castle foyer later that evening to meet with Celestia and Luna.

"As you already know," said Luna, "we've called you for your help in something entirely different from what you're used to. It appears that I have lost my ability to traverse through the dreams of my citizens. I had many attempts in the prior evening, but not once did I escape my own nightmares. I need you to traverse through my dreams to find the root of the problem, or the ponies of Equestria may never benefit from my protection ever again."

Twilight and Starlight appeared uncomfortable. The letter that had been sent to her said nothing about the rest of her friends except for Starlight. "Why only us? Can't the rest of our friends help as well?"

Luna sighed, and Celestia answered for her. "Unfortunately not. Unlike the Tantabus, whatever nightmarish manifestation has rooted itself into my sister's subconscious is much more dangerous. The Tantabus flowed freely through Luna, escaping into the dreams she visited. This other creature operates in the opposite fashion. It closes the link Luna has between herself and the citizens of Equestria, making it impossible for her to traverse their dreams."

"The reason your friends cannot come along is that my powers are drastically weakened," said Luna. "My mind simply cannot support any more than one or two visitors, and even so it needs to be one to whom I am close."

Confused, Twilight replied. "But...wouldn't Celestia be a better option? You two have been sisters for...well...millennia."

Starlight appeared uncomfortable. "I've only been friends with Twilight for a fraction of a fraction of that time...and I honestly...don't know you all that well..."

"That may be true," said Celestia, "but we both decided this way was best. Twilight has always been close to me and my sister, and you, Starlight, have a fair amount in common with her. But there is one more wrinkle to this problem. Somepony will need to keep watch in the real world to do whatever they can to keep things running smoothly, and that will be me. If at any point Luna awakes from slumber during this process..."

Celestia had put a hoof to her head, unable to speak the words she wished to say, so Luna continued. "I may not wake up for a long time."

"What do you mean by a long time?" Twilight asked with concern.

Starlight continued with another question. "Like...a coma?"

Celestia sighed. "I think it would be best that we don't focus on what could happen. I have faith that my most faithful student, along with her friend and pupil, will be capable of completing this task. Come and let us arrange the bedroom to begin. It's almost time for the moon to rise."

Celestia and Luna led them to the bedroom and arranged two beds beside Luna's. Luna had briefly left to perform her daily ritual of rising the moon into the sky while Celestia spoke to Starlight and Twilight.

"I know this is a large burden to put upon you, but I am hopeful you'll be able to help her and find the root of this problem."

Twilight nodded. It was true this was a vastly different undertaking compared to what she was used to, but she had been through much worse. Starlight, however, nervously slipped into the bed on the opposite side of Luna's. Thoughts of worry began surfacing in her mind as Celestia continued preparing while Luna returned to the room. The moonlight shone down through the beside window and illuminated the blankets upon her mattress.

"Are you ready?" Luna asked as she laid down to rest.

They nodded and got comfortable. Starlight wondered briefly how they were expected to just fall asleep on a moment's notice, but her thoughts quickly became foggy as tendrils of dark magic rose into the air out of Luna's horn. Eerily seeping through the air like wisps of smoke, the tendrils found their way into Twilight and Starlight's foreheads, almost immediately causing their eyes to close shut.

Celestia watched with concern on her face as they began to sleep. She would have to do everything in her power to make sure they didn't wake up prematurely, as what she couldn't bring herself to tell them earlier was that doing so would trap them inside Luna's eternal nightmare as well.