“This vault was created with an extreme amount of protection; no doubt you can feel a small fraction of it.” Twilight nodded in response to Celestia, “it is, literally, impossible for any being to break into this vault… however every rule has an exception, and in this case there are only thirteen exceptions in all of existence, and they are all gathered in this castle.”
“You don’t mean…” Twilight began, the sisters nodded.
“One of the princesses stole the Aether Key. One of the princesses is a traitor.”

When Twilight attends her first royal summit, all hell breaks loose and the fate of the world is put on the line when an ancient artefact is stolen from the deepest vault in Canterlot Castle. Now, not only Equestria, but the entire world rests on the shoulders of Twilight and her friends, but with the clock ticking and the end in sight, the elements of harmony may not be enough… that's where Clarity comes in.

The cover picture is only temporary, I may change it later if I can get a better one made