(All characters begin in the Castle of the Two Sisters at the Summer Sun Festival, mere minutes before the sun is to be risen by the illustrious Princess Celestia to begin the longest day of the year.)
As everyone enters the castle (the open invitation had been spread far and wide across the realm), many different races of ponies are seen, including a sea pony, and even a gryphon! The hustle and bustle of the crowd at an event like this is something rarely seen in all of pony history, and both it and the castle are truly spectacular to behold, despite the inherent gloominess within the surrounding Everfree Forest. Guards check everyone’s belongings at the door, specifically demanding any kind of items that could be used as weapons to stay in their possession as long as you are in attendance.
Autumn Draught enters the castle, thrusting her belongings upon a guard before dashing off towards the gardens to put as much distance between herself and the crowd as possible. Sunny Beach, receiving a plethora of gazes due to her enthralling beauty, seems to enchant everypony she passes. With sea ponies being a rare sight for anyone, her beauty and intrigue earn her a considerable amount of attention. Guidmulo enters the castle as well, causing quite a stir. The guards allow him to pass, despite considerable consternation visible on their faces, and many ponies, particularly ponies who had been alive during the war, glare at him with uneasy expressions. This tense wave of attention doesn’t seem to affect Guidmulo at all, as he gleefully begins his search for a dessert table (but fails to find it.)
Princess Celestia is regally perched upon her throne, warmly smiling and chatting with individuals who had formed a line in front of her to speak with her and obtain autographs. Next to her is Starswirl the Bearded, a famed wizard who seems not particularly comfortable with this kind of party environment. Though his garb makes him easily recognizable, his appearance is quite striking, but he nonetheless remains dutifully by Princess Celestia’s side. Princess Luna is present, but she appears to be pacing back and forth near her throne, not really speaking with anypony.
Sunny Beach joins the line to speak with Princess Celestia, the Princess she worships and loves, while Guidmulo continues to search for sweets and Autumn sips cider outside, uncomfortably observing those in the party. As Sunny approaches the Princess, she kneels and declares herself as an oracle, asking Princess Celestia why she had been chosen, and referencing her cutie mark. Celestia smiles and assures Sunny that she must have a great potential within her, while Starswirl is suddenly quite interested and awkwardly begins examining Sunny’s cutie mark. In the midst of this, Sunny notices Princess Luna is wearing a clearly upset expression on her face.
Princess Celestia excuses herself from conversation with Sunny, and rises up. With a magically amplified voice, Celestia declares that it’s time to bring forth the sun and begin the longest day of the year. Her horn begins to glow a majestic gold, and through a massive window behind her, the sun begins to come up and bring forth the day. Everypony cheers and clops their hooves on the ground happily.
Shortly after the moon has disappeared beneath the horizon, some ponies begin to notice that Princess Luna is no longer present. Starswirl whispers something to Princess Celestia, and the two of them suddenly depart up a guarded staircase and through doors on the southern side of the Great Hall. He could be heard by Sunny Beach mentioning that something didn’t feel quite right.
Autumn had been in the rear of the Hall to watch the sunrise, and noticed Princess Celestia and Starswirl hurrying off. She begins to sense the magic around her, and feels some strange, otherworldly power. Something was simply wrong about it, and she knows she needs to act. Attempting to find the source, she gallops straight to the most suspicious character in the room, Guidmulo, and begins sniffing him. Sunny, who had been nearby, inquires as to Autumns actions and expresses a desire for friendship. Unaffected by Sunny’s charms, Autumn refuses her and runs to the staircase, demanding that the guards let her through or summon Starswirl. Sunny and Guidmulo follow.
After some arguing, a guard runs up the stairs to retrieve Starswirl and Celestia, but by the time they emerge from the room, a figure suddenly teleports from behind Luna’s throne. It was Luna herself, and a dark expression is on her face. Angrily, she exclaims at Celestia, condemning her sister for the praise and love ponies gave her for the day while her and her night was ignored, and that there can only be one Princess in Equestria. At that, a darkness suddenly envelopes Luna’s body, and she transforms into a dark pony bearing armor and an evil expression. Guidmulo notices she is also suddenly wearing a strange, unrecognizable necklace, while Starswirl mutters under his breath that he should have seen this sooner, and that this isn’t Luna anymore…
Luna, now calling herself Nightmare Moon, suddenly uses her magic to raise the moon in front of the sun, bringing darkness. Blasting a hole in the wall where the moon was visible to those in the Great Hall, dark shadows come forth from the moon itself, manifesting on the ground all over amongst the ponies. Touching some, the ponies that were struck didn’t get hurt or die, but rather suddenly collapsed on the ground and seem to be sleeping.
Starswirl immediately demands that everyone leave, and most of the ponies in attendance begin to flee the Hall in a panic. Guards move forward and begin stabbing some shadows with their spears. Autumn makes a bee-line for the door and retrieves her pack from the guard’s storage room, producing her vials to quickly make bombs that engulf the shadows in flame when struck. Guidmulo begins swooping past the shadows, picking up ponies and carrying several of them to safety (although they probably would’ve preferred he at least given them a somewhat softer landing.) Sunny is able to gently heal some ponies that had been forced asleep by the touch of the shadows, stuck in some awful nightmare.
While the battle and evacuation continues, Celestia battles with her sister, both using god-like forces from their horns as they fly around. Though Nightmare Moon is able to summon more shadows, Starswirl is able to kill more than one with a single attack, and helps to save many. Celestia seems to really be holding back, reluctant to fight her own family, until she is struck to the ground. In response, she magically opens a hole in the floor of the Great Hall, a stone statue with smaller stones around it lifting out of the ground. These items are revealed to be magical gems known as the Elements of Harmony, and Celestia uses their power to absolutely overcome Nightmare Moon.
After Nightmare Moon’s defeat, Celestia collapses to the ground, crying. Autumn snaps at Starswirl to go to her, and assists Guidmulo in finishing off the remaining shadows. Guidmulo, recognizing that this seems more violent that he thought a pony celebration would be, is questioning whether or not this is normal for a festival. Sunny runs to her Princess’s side, doing what she can to comfort her as well. Starswirl then notices a shimmer where Nightmare Moon fell, and begins casting a complicated spell that moves this shimmer into the moon itself. A face appears in the moon… The Mare in the Moon.
With the danger gone, Autumn collapses to the ground in hysterical tears as well, her Princess that she worshipped suddenly transformed into some evil thing and now essentially gone. The damage to the castle is very severe, and the sadness in the eyes of the ruler that all of Equestria looks to can’t be overstated.