The story so far:
Twilight is summoned to Celestia's castle on a mysterious errand and puts Fluttershy in charge of rallying group solidarity while she is away. We learn how Rainbow Dash, after suffering humiliation at the hooves of Rarity and Sweetie Belle, has found a new direction in life and is eager to avail the get-together for her madcap purposes.
Meanwhile (in this latest installation), Twilight arrives at her parent's house and makes her way to the castle in the morning. Therewith she encounters a mystic figure from her past who offers to guide her through the transformed city...