The white walls of Canterlot gleamed in the midday sunlight. As Equestria's capital, the city displayed some of the finest architecture in the country, commissioned by Princess Celestia after the castle in the Everfree forest was abandoned.
With the return of Luna from exile, the Equestrian government had required some rearrangement to allow for the younger alicorn to rule alongside her sister. Most of the day, the two found themselves up to their necks in matters of state in some form or another, but at this moment, the two were sharing a rare moment together, appreciating the escape from schedule for what it was.
Unfortunately for them, the calm wasn't to last.
A loud rumbling filled the princesses' quarters. Celestia and Luna stood up, eyes looking for the source of the sudden noise. Their question was answered when a wooden blue box slowly faded into existence in front of them.
Luna shrank behind her older sister, afraid of what the box might bring. Celestia simply looked on in confusion.
The box's door opened, and a blue-suited brown colt stepped out. "And that," he said, seemingly to no one in particular, "my fine equestrian friends, is the only way to travel."
Applejack stumbled out of the box. "I'll stick to my own four hooves, thank ya kindly."
The princesses' confusion grew as the remaining five bearers of the Elements of Harmony all exited the box with similar discomfort (save for Pinkie Pie, who insisted that they all ride again), ending with the purple unicorn Celestia knew very well.
"Twilight Sparkle!" she gasped. "What is the meaning of this?"
"Princess Celestia!" the six mares quickly bowed. Twilight shot a glance at the colt. "You didn't say we were going to land in her bedroom!" she hissed.
"To be honest, I didn't know, either." The colt muttered, glancing back at the box they arrived in. "I wish he'd tell me these things more often. I almost think she enjoys these awkward situations."
The colt approached the dumbstruck princesses with a smile and kneeled. "You must be the Princesses Celestia and Luna. I'm the Doctor; very pleased to be in your audience –"
"Princess!" Three royal guardsponies burst into the room. "We heard noises and –" The leader caught sight of the seven ponies. "You! How did you get in here? Who –"
"Stand down, captain," Celestia said calmly. "These are my…" Her gaze lingered on the Doctor. "…friends. They are welcome."
The captain gave the Doctor a suspicious look before leaving with his subordinates.
"Now then," said Celestia, facing the group, "Perhaps you can explain your sudden appearance in my chambers, Twilight."
The purple unicorn mumbled several false starts before pointing at the Doctor and panicking. "It's all his fault! It wasn't until he showed up that weird things started happening and all this stuff about aliens and Time Lords and boxes that can fly and – and – and –"
"Calm yourself, Twilight," The Sun Princess interrupted. "I'm not mad at you, just…perplexed."
Celestia walked towards the Doctor. "It seems my student believes you to be responsible for this, Doctor. Would you care to explain?"
"Certainly," the colt replied, moving so he stood between the six mares and the two princesses. "Now, I'm sure you are at least partially aware of the situation in Ponyville?"
Celestia nodded. "Twilight informed me of a sickness almost a month ago, but I haven't heard anything since."
"Well, then I think you should know that it has spiraled spectacularly out of control thanks to a bunch of mind-infesting things called empathivores."
Both of the princesses stiffened at his final word. The Doctor's gaze hardened. "But you would know all about them, wouldn't you?"
"What in the hay is that supposed to mean?" Applejack asked.
"Empathivores don't just come out of nowhere," the Doctor explained. "And they're an awful long way from home…" He focused his gaze on Luna. "…which means someone brought them here."
Celestia blocked her sister from the colt's view. "She didn't know! We thought they had been –"
Celestia stopped, surprised that her sister had spoken up. "I think…it would be best if I explained it to him." She looked at her hooves. "After all, this is partially my fault."
The Sun Princess hesitated, then dipped her head in agreement. Luna stepped forward, wary of the Doctor's gaze.
"Over a thousand years ago, I ruled over Equestria alongside my sister. It was a different, smaller kingdom back then, but we still ushered the sun and moon as we do now. It was a good life, but as I looked at our subjects, I began to resent my role. The ponies worked and played under her sun, but when the moon came into view, there wasn't a soul awake. The more I saw that pattern, the more I began to believe that Celestia was loved, and I was not.
"Naturally, I grew jealous of her, but for months, I never dared to admit it. I tried to ignore it, to simply do my duty as always, but those feeling never truly went away.
"But it all changed in one night. As I raised the moon, I felt something new in the night sky, an object unlike anything I had seen before. A ship made of metal, floating through space! I reached out to it, and found the creatures you call 'empathivores.' They had taken control of the vessel's original crew, but those bodies had long since died, leaving the ship adrift as I found it.
"As we conversed, they sensed my long-dormant jealousy, and saw an opportunity. They asked that they would be allowed to enter my mind, promising to help me get the respect I thought I deserved." The dark mare shuddered. "Like a foal, I agreed. The came into me, and immediately, I heard their thoughts among mine, whispering to the darkest parts of me to bring them out. I used my magic to become Nightmare Moon, and refused to lower the moon the next morning."
"So when you were Nightmare Moon, it was really the empathivores in control of your body?" Twilight asked.
"No." Luna said without hesitation. "I was in full control during the whole ordeal. There were a great influence, but I was still the one responsible for my actions.
"Anyway, you all know what happened next. Celestia immediately sensed the dark presence in my mind. The Elements of Harmony were her only weapon, but she could not use their full power – that was meant for chosen ponies such as yourselves. Using what power she could, she trapped me on the moon I once governed."
"A spell that would last one thousand years." The Doctor turned to Celestia and frowned. "One. Thousand. Years. What did you think would happen? The empathivores would die? Luna would break free of them? But no; they remained. They had Luna to feed on, and she had a lot of life and anger left in her. And she sat there, waiting those thousand years out, as those monsters chewed on the corners of her mind. She could have gone mad from that, Celestia. For all you knew, she could have died!"
"I know, Doctor," Celestia replied, looking at her sister. "And not a day has gone by since then that I wished I hadn't."
"Sister…" The two princesses nuzzled, Celestia wiping the tears from Luna's eyes.
"But what happened?" Rainbow Dash asked. "Obviously they didn't die; so why are they only showing up now?"
"When you defeated Nightmare Moon, you forced them out of Luna's body," the Doctor explained, "but you didn't kill them. They must have been weakened considerably, so they probably have been piggy-backing in some ponies' heads until they recovered; they were most likely the first to fall ill."
"And I gather by your presence that things have taken a turn for the worse?" Celestia asked.
The door was burst open by the same guards from before. "Celestia! My lady, there's a mob of ponies marching to the gates! Something's wrong with them – their eyes… they're all red!"
"I think that answers your question," said the Doctor.
A full regiment of Celestia's royal guard lined up in front of the castle gates. Before them, the empathivore-controlled citizens of Ponyville marched towards them, almost daring the princesses to act first.
Fluttershy shivered behind the Doctor. "Those poor ponies…w-will they do that to us too, Doctor?"
"Not if I can help it," the colt replied.
The cream-colored mare looked into the Doctor's eyes in amazement. "Aren't you afraid of…monsters?"
The Doctor winked at her. "No, Fluttershy; they're afraid of me."
He waked over to Celestia. "I need you to hold them off as long as you can."
"We will do what we can," Celestia replied, "but I refuse to hurt my little ponies."
"I don't expect you to," said the Doctor, walking away. "Come along, Twilight, Rarity, Applejack, Rainbow Dash, Fulttershy, Pinkie Pie. Blimey, that's a mouthful. You ponies need a team name or something."
"I can assume you have a plan, Doctor?" Celestia asked.
"Not yet; working on it!" he shouted over his shoulder.
The Doctor led the six mares a few rooms down the hall. "Right, I need to go fetch the TARDIS. Don't go anywhere, I'll be right back."
He ran off down the hall. A few minutes later, the blue box reappeared in the room, and the Doctor emerged carrying a strange object.
"So, it took a generous disregard for conventional laws of physics and my best coffee maker, but I believe this will work." He placed the device on the floor. It was shaped like a tower, with small bits of metal sticking out like tree branches. The top pulsed a rainbow of colors and six helmets were attached to the base by cables.
"And just what in the hay is that s'posed to do?" Applejack asked.
"The reason why the empathivores didn't get to you," he explained while making adjustments of the device, "is because you six hold the Elements of Harmony. You need to generate energy to cover the whole planet to get them all."
"The whole planet?!" cried Rainbow. "How do you expect us to do that?"
"That's where this baby comes in," the Doctor replied, patting the machine. "You six wear these helmets, and it will multiply the energy and release it in one big bang." He handed out the helmets to the six mares. "In theory, anyway."
"In theory?" Twilight asked incredulously.
The Doctor scratched the back of his head. "Well, I haven't actually seen the Elements in action, so all I had to go off of was the readings I took from you earlier and your descriptions of how it worked, so…" He trailed off as the mares looked at him fear in their eyes. "It'll work! I promise!" he affirmed with a smile.
Pinkie Pie narrowed her eyes at him. "Do you Pinkie Pie Swear?"
The colt raised an eyebrow. "Do I what?"
Pinkie moved until there was barely an inch between them. "Cross you heart, hope to fly, stick a cupcake in your eye?"
"Okie Dokie Lokie!" Pinkie smiled and bounced back to her helmet.
The sound of something colliding with the castle gates echoed across the room. The Doctor clapped and rubbed his hooves. "Alright, girls, we haven't got much time; let's get to work! Allons-y!"
The guardsponies struggled to put their weight against the gates. The castle was not built to withstand a siege of any kind, as Equestria had not known war for over a thousand years. Though the guards were well-trained, their expertise lay in non-lethal combat; the empathivores were willing to use their pony hosts to kill if necessary.
The captain of the royal guard made a hurried bow as he approached Celestia and Luna. "My ladies, we are doing what we can, but those…things won't let up. We can't hold the gate much longer."
Celestia nodded. "Reinforce the gate as much as you can, then fall back. We only need to keep them from the Elements and the Doctor."
The captain saluted and made his way back to the stallions under his command. Luna looked up at her older sister. "So much rides on that colt…do you think his plan will work in time?"
Celestia looked down the hall the colt had run down earlier, where he was doing something she couldn't discern. "I don't know," she answered, "but when I look at him, I get a feeling…that even though I just met him, I could trust him with anything."
Luna gave Celestia a small smile. "I know, sister. I get that feeling, too."
And so the Princesses of Day and Night joined the guards and watched the gate, waiting for the Doctor's plan to unfold.
Though her eyes were closed, Twilight could practically see the Doctor pacing nervously around them. The sound of the gate collapsing and soldiers fighting in the hallway had given them all a sense of urgency and a worry that the machine was not working fast enough. The meter on the device was so very close, but it moved agonizingly slow. They were cutting this too close.
A sudden shout came from the hall. The mares opened their eyes and saw four empathivore-controlled ponies had found them and were running towards them.
The Doctor stood between them; the determined look on his face told his intentions to all.
Twilight reached to stop him, but was too late. He charged the ponies, undoubtedly too aware that they could toss him like a rag doll.
A wave of emotion came over the six, and with it, the meter hit 100%.
The light from the machine glowed brighter than the sun as a rainbow of energy cascaded from it. It flew with such force that every pony in the castle was knocked of their feet. The wave continued wiping across the planet until it met on the opposite side with what would later be described as a "reverse rainboom."
The last thing Twilight saw before falling unconscious was the Doctor's wonderful smiling face.