Twilight's just a little nervous. It has nothing to do with Moondancer taking over the Castle Library. Or Moondancer's smile when she suggested taking over the library. Or anything to do with libraries. It's nothing. Nothing at all.
After the events of "The Cutie Remark," Starlight Glimmer develops a new respect for Twilight when she discovers that they both have something in common: that they once had sanctuaries that were both destroyed.
A gigantic robot from space is stalking Equestria destroying everything it sees. Meanwhile, Twilight is more concerned with finding a copy of a book about moths. Yes, it's going to be another one of those days.
From her new castle, Twilight can't stop staring at the spot where the library tree used to be. But Ponyville is an earth pony town, and tall oaks from little acorns grow.