Batsy Fluffentuft (not the most respected of the lunar guards, and in fact on super-probation from Princess Luna herself) manages to escape into the town of Canterlot and have herself an adventure.
A troubled Princess Celestia, wandering her School for Gifted Unicorns late one night, chances upon her young faithful student, Twilight Sparkle, who has problems of her own: she can't catch the Tooth Flutterpony.