When Twilight visits Celestia's private hall of stained glass windows, the portrait of an ancient astronomer catches her eye. Who was this pony? Why was she so important to Celestia? And why does she look so familiar?
Celestia and Twilight are in a relationship. Twilight wants to meet Celestia's parents. Celestia, understandably, is terrified. After all, it's always awkward when one's parents aren't exactly ponies at all.
Celestia has seen a lot of terrifying things, but nothing she has ever faced is more terrifying to her than this: Telling Twilight's parents she's in love with their daughter.
Twilight and Celestia don't have dates for Hearts and Hooves Day. Luna looks to change that, and Twilight and Celestia find the date to be more than they bargained for.
Being turned into a fully grown alicorn was bad enough. But having to contend with a sudden interest from her mentor that reawakens long forgotten feelings? Twilight's life just got a whole lot more complicated.
Twilight finds it a bit difficult to reconcile Celestia's playful new manner with the regal teacher she knew for so long. Once she does, however, the benefits are plain to see.