Though the Canterlot castle appeared to be incredibly large in size, in actuality it was significantly more so.

Canterlot was built onto the side of a mountain. The reason for this was that it did not used to be a city for high class society, let alone be the capital of Equestria. Canterlot used to be a mining camp.

Thousands of years ago, Unicorns used to store magical energy inside a special kind of crystal. Once enough was stored, this energy could be used to power all kinds of advanced technologies: Portals that broke the fabric of reality, machines able to control the minds of living things, weapons of mass destruction able to kill the immortal - the possibilities were endless. As such, those crystals were incredibly valuable, valuable enough for kingdoms to rise and fall over any kind of misuse. Over time, all but seven of the most powerful had vanished.

Out of need more than want, Princess Celestia had her people searching the world for deposits of those crystals. Many years of searching beared no results, until one fateful day, they found it: The Hollow Mountain. One of the largest mountains in Equestria. Inside, a seemingly endless cave system filled completely with those magical crystals.

That little mining camp became a sizable mining town, which became an enormous mining city and, finally, became the capital of Equestria. For a long time, the city was built partially inside the mine. Over time it expanded and retracted, eventually snailing its way through the caves until it became the floating city, sitting on the edge of a mountain face.

About two hundred years after Princess Luna’s banishment, the cave system, drained of all crystals, was finally closed. What few knew is that this was simply part of a plan of Princess Celestia’s.

Dozens of secret tunnels were dug in the belly of Canterlot castle, all leading into the great cave system. Trillions of bits worth of top secret equipment was moved though those tunnels, and the empty cave eventually became Princess Celestia’s secret laboratories. It was in those secret labs that the Princess’s science specialists worked to create and hoard technology, magical and otherwise, hundreds of years beyond that seen in modern society. Things so advanced, a simple Pony would call unholy - and they wouldn’t be wrong. In those labs, everything was permitted. There were Ponies bred there for the sole purpose of either being live test subjects or to be harvested for their organic parts.

Obviously, secrets of those levels were policed at the highest and most brutal of levels. If a citizen ever discovered those labs, they would be harvested for parts. If a scientist working at those labs ever had the slightest thought of wanting to leave, they would become a test subject. Those labs were easily the best kept secret in all of Equestria. Only one unauthorised Pony had ever set foot in there and managed to escape, but, alas, this is not her story and it is not important.

What is important is what was happening in a certain hospital room:

“I believe I shall be fine without your guards,” Princess Luna lit up her horn. “I have guards of my own, after all.” A flash from her horn teleported two of her own guards into the room.

“...Very well.” Princess Celestia left the room and her guards followed. After ordering some of her guards to stay and spy on the room, the Princess made her way directly to her secret labs, taking all of the DNA samples she had gathered along with her.

Luna’s excuse to take him won’t change anything, she thought as she walked through the dark passageway, even if I cannot have my pawns experiment on him directly, the DNA I have gathered shall be more than enough to discover the source of his strange magic. Princess Celestia smiled to herself. They were correct about his reaction to the fear poison, after all.

In Twilight’s tower, Cloud had just received some particularly interesting news.

“You think Celestia poisoned me?” Cloud asked.

“Yeah,” Twilight replied. “I have a small amount of evidence but, before I can go into detail, I need… Um...” Twilight broke eye contact and coughed into her hoof. “Samples.”

“Blood or urine?” Cloud sighed.

“...Both, and, uh, more.”

There was a pause.

“...How much more?”

“I’ll, um, write a list.” Twilight walked downstairs to write a list and collect a few tubes and needles for the samples.

Cloud turned to Princess Luna, who had been using a telepathy spell to give her guards their orders as to not interrupt his conversation with Twilight.

“So what’s gonna happen?” Cloud asked. “Even if I was poisoned, I still…” he gulped, “killed someone. I don’t understand how I can go unpunished without becoming a fugitive or something.” He sighed. “I don’t really understand anything that’s going on right now, honestly.”

“I have use for you, Cloud Calculation,” Princess Luna answered as her guards moved to a more appropriate area in the room to stand guard. “I do not know what my sister is scheming, but I know that she never does something without reason-”

Meanwhile, in an alternate universe…

“Yes!” Celestia screamed. “I know that it must be you who is the sandwich terrorist! It was a cheese sandwich!"

Luna looked confused.

"Watcher, arrest her immediately for assault on sandwiches!" Celestia threw Watcher at Luna, missing and hitting her favorite mirror. It shattered into many pieces, plenty perforating Watcher’s spleen.

Watcher screamed.

“-and that is what makes her dangerous,” Princess Luna continued. “If we allow her to continue her plans without interruption, I have no doubt that one or more of us shall feel nothing but despair.

“What happens next is that you must increase the speed of your training, both magical and physical. You shall stay in this tower: By day, Twilight shall train you, focusing on offensive and defensive magic, but by night I shall continue to train you in the art of fighting.” She paused for a moment. “You managed to learn the dislocation move I taught you after a single session. This is impressive.”

“An empty head picks stuff up like an empty bucket picks up water, I suppose,” Cloud muttered, gazing off to the side.

“Then you should ‘pick up’ some better analogies.”

“Eat a dick.”

“The reason for these actions may be tough for you to bare.” She began to pace. “A thousand years ago, society was… somewhat less civilised than what you are used to. Because of this, my sister and I introduced a… new court proceeding. Not mandatory, of course, yet highly effective.”

“Skip the drama, please,” Cloud groaned, “just tell me what I’ve gotta do.”

The Princess stopped pacing and looked him dead in the eye.

“Trial by combat - to the death.”

There was a long pause.

“I… have to kill again?” Cloud heart rate picked up.

“Only death can pay for death.” Princess Luna began walking to the door. “At most, I can delay for a fortnight. In the meantime, you must prepare as well as you can.”

“This... Is this the only way?”

“Yes, this is the only way you can walk as a free Pony.”

After a moment of trying to comprehend what he had to do, Cloud nodded.

“Then I… I trust you.” He took a deep breath and quickly released it. “If it has to be done, then so be it.”

“Very good.” For the first time in a millennium, Princess Luna gave a smile of honest respect. “I shall leave these two guards here for the moment, for I cannot be certain of the safety of this tower. I am sure they will introduce themselves in due time. In the meantime, I cannot contact you outside of the dream realm. Study hard and survive.” The two shook hooves. “Until tonight.”

Cloud gave a determined nod as the Princess teleported away.

Kill again, huh? If I can figure out how that new circle works, it shouldn’t be too difficult. Criminy, what have I gotten myself into...?

A few seconds later, the door opened and Twilight came back inside levitating vials and needles - about a dozen each - as well as roll of parchment.

“Sorry I took so long; turn out I hadn’t washed these since-” She stopped, noticing the Princess’s absence. “Did she leave?”

“Yeah,” Cloud replied. “She explained what I have to do.”

“Good. Take these,” she moved her carried items forward slightly and Cloud took them with a telekinesis spell of his own, “I’ve made a list of what I need.”

Cloud had a quick look over the list. Oh jeez-!

“Seriously?” He asked, sounding exasperated. “You really need…?”

“Y-Yes!” Twilight stammered, her cheeks reddening slightly. “I need to know what kind of poison was used! I have no idea how it could have been administered!”

“I don’t know if if I… can… y’know. Not without...”

There was an awkward silence in which Twilight did a wonderful impression of Applejack’s brother.

“There’s, um, magazines under my bed. Use those.”

Cloud coughed into his hoof.

“R-Right…”

After a few more moments of awkward silence, Cloud walked away towards the bedroom to collect his samples.

Twilight tried to clear her mind of the sticky situation.

Author's Notes:

There's more foreshadowing in that opening than you'd believe.