Erised stra ehru oyt ube cafru oyt on wohsi

These are the words etched above the magic mirror filly Twilight finds in the Canterlot Castle. Her counterpart, Princess Twilight, finds this same phrase in her own world. Uttering the phrase allows them to meet face to face, and, both enamored by the possibility of a life they can only imagine, the two agree to secretly switch places for a bit. They promise to return to their proper worlds in two days time, before they can be found out.

That promise, like their secret itself, will prove very hard to keep.