Twilight Sparkle, a student of Princess Celestia, was sent by the majestic ruler to a poor section of Canterlot. This section is known to all ponies as the Queens. No pony in the right state of mind would live in that sector and not because of it being poor.
Many fear it for reasons even Celestia does not know.
And…
Twilight sees the reasons unfold before her very eyes…

This exists before season three begins.