Five years. That's how much time has passed since Twilight Sparkle had uncovered the secrets contained within Starswirl the Bearded's journal. Each piece of the code now solved, Twilight had felt the need to train herself under the tutelage of Princess Luna, before she could attempt to perform the spell that the code had hidden. It was a scrying spell of sorts, but unlike most spells of that type, it contained elements and geometries the likes of which Twilight had never before encountered, and she considered herself an expert. This particular spell was also linked inexplicably to Starswirl's final experiment.

Starswirl was last seen throwing himself into a gateway of his own creation but of which he had lost control. That final, desperate act to keep the rift from expanding and taking the whole world with it, had been witnessed by none other than Twilight herself. In the aftermath, Starswirl's sacrifice had managed to produce a single, immensely-powerful crystal, which had been locked away in some unknown location in order to keep it out anypony's hooves. If she was to perform her newly discovered scrying spell, however, Twilight needed that very artifact. In fact, it was the only ingredient which she now lacked.

Twilight suspected that it would be buried deep underground within some magically sealed vault, along with other powerful artifacts. It's even possible that Discord's Statue was held in one such location at one point in time. Twilight knew that Princess Luna would know the artifact's exact location and that was part of the reason she had decided to make the Alicorn of the Night one of her mentors, and after knowing the princess as closely as she did now, Twilight was finally ready to put her plan into action.

The plan started with a simple but dangerous magic of Twilight's own design. The main goal in creating the spell was for it to be deemed too dangerous to be published publicly, but still viewed as possibly useful in the future, ensuring that it would be stored in very same vault as her target. Using some modifications, most no different than some of the same tricks that Starswirl had used in order reawaken himself from his hibernation, Twilight had enchanted the parchment, on which the spell was written, with a tracking glyph. The glyph would pass through any magical barriers unnoticed because it was designed to only respond to the energy contained within Starswirl's Stone, which is what the artifact she sought was now called. Once the stone was found, a matching glyph would alert Twilight to its location.

A location that Twilight was currently standing in front of at this very moment.

According to the guardsponies stationed outside the entrance, the hidden vault was one of the very few places left within Equestria that Twilight was not allowed entrance. They told her that they were under direct orders to ensure that nopony, save the Princesses Luna and Celestia, should be allowed to enter. Those guards now lay on the ground, unconscious and hopefully with no memory of Twilight's presence.

"I'm sorry I had to do that, but I've come too far to turn back now," she said, apologizing to the guards as she finished the spell. They never stood a chance.

She approached the carefully hidden magical barriers next. While she had no idea what kind of spells were going to be used, the barriers would also prove to be no match for Twilight. Only the first barrier was supposed to keep others out, anyway, the rest were designed to keep powerful things in. Before long, she had reached the main storage room.

All around her, covering almost every available inch of space, were numerous, unmarked wooden boxes. Some of the boxes were as large as a house, while others were small enough to rest upon the many shelving units that had been arranged in rows. Twilight suspected that her quarry lie within one of the smaller boxes.

Everything in the room seemed to emit some sort of arcane energy or another, but the crystal she needed had a unique energy signature, one that she had only experienced once before, back when Starswirl had initiated the experiment leading to his demise. The energy was unlike anything else in the world, and seemed to disobey every single law of energy conservation that supported the basics of magic use. Twilight often wondered if Starswirl had any explanations to that particular effect. What little of his research she was actually allowed to look at, contained nothing regarding his final project. It was partly why she was so adamant about solving this puzzle in the first place.

After she cast a quick search spell, she located the box which contained Starswirl's Stone. As she removed the box from the shelf to get a closer look, Twilight accidentally tripped a sensory spell located underneath the box. There was likely to be one underneath each and every one of the items in the vault, all of them set to trigger the alarm. No doubt, reinforcements would be arriving soon to apprehend her.

Twilight was prepared for such a possibility however, and soon she had the glyph she needed for her escape carved into the stone surface of the floor. Using a trick she had learned from her studies of Starswirl's research, Twilight poured a red substance, called Flux, into the crevices of the glyph. When she activated the associated spell, everything in the immediate area would trade places with the area surrounding an identical glyph she had prepared earlier.

Soon, she was safely outside the vault. As an added precaution, she destroyed the Glyph that she had just made by carving an even deeper gouge into its surface, the Flux draining into the new trough. This would effectively keep anypony from simply recasting the spell in order to follow her. Twilight's knowledge of the artifact's existence would eventually draw suspicion towards her, so she made haste towards her secret laboratory in hopes that she could solve the puzzle once and for all.

A final mystery that Starswirl had somehow managed to leave for her, this enigma had plagued her for almost half a decade. Now with Starswirl's Stone located within it's proper place, Twilight cast the Scrying Spell in accordance with the cryptic instructions left to her, in hopes that answers would soon be forthcoming.

Royal Canterlot Archives:

Since the alarm had been triggered the Royal Sisters had been on high alert. Initially they had believed in the possibility of one of the artifacts had activated itself, and had taken actions against such a threat. After all, who would be capable of breaking into a secret hidden vault that only a handful of ponies, in all of Equestria, even had a suspicion of existing?

When the contingent of soldiers arrived on-site along with Princess Celestia, they feared for the worst upon sighting the guards lying before the entrance. Relief was short-lived upon the discovery that they were only left unconscious. Celestia entered the vault with only a cursory examination of the now-failed barriers. The only evidence that was forthcoming at the moment was the singular crate was not where it should be, and the glyph carved upon the floor. The patch of floor surrounding the glyph no longer matched that of the rest of the vault, indicating that it had been a one-way translocation.

Identifying what exactly had been stolen would take some time, as the inventories were kept in a separate location. That, along with the fact that all of the crates located within the vault were left unmarked in any way, was a method to help prevent such a crime. The only thing that Celestia could do, was attempt to activate the Translocation Glyph that the thief had left. When this too failed, she evacuated the premises and resealed the vault, barriers and all.

She suspected that any thief as adept at covering their tracks as this, wouldn't take any chances at leaving anything for the outside guards to be able to identify them with, but she had them debriefed and replaced immediately. While anypony could theoretically create the Translocation Glyph, only a unicorn of significant skill could thoroughly alter the memories of the guards, or even break through the magical barriers so cleanly.

Later, when Celestia returned to the castle, she had her sister retrieve the inventory list so that they might find out what went missing. To both their surprise, the missing item was something that very few ponies knew existed, and even fewer than that would know what it was capable of. Not a single one of those ponies was supposed to know that the vault existed, however. The list of possible suspects was in the single digits.