A long time ago, humans walked the earth. They're all gone now, either dead or turned to ponies by the many "Conversion Bureaus." Now it's the ponies that govern the world, led by their goddesses, Princess Luna and Princess Celestia. Very few remember or give much thought to the days of humanity.
But sometimes things don't die very easily. Sometimes things linger, even if it's just a memory or a legend. Sometimes when an egregious injustice has been left unchecked, even a pony can get very angry.
On the crew of the White Rose there are many such angry ponies, led by Firebrand. These are young students who have perceived an injustice and are determined to blow everything open with one blazing truth.
Based on "The Conversion Bureau."