The Shadonian race is an ancient kind of Equestrian ponies that all but vanished 1000 years ago when Discord brought terror and destruction in his quest to take over Equestria.
Only a handful of Shadonians survived including our main character, Queen Isa, who was just a filly princess at the time. She, her uncle and a few citizens fled underground as their kingdom was destroyed.
There they stayed for over a millenia, living in secret when every other being thought they had died out.
Once Isa became a Queen, she decided enough was enough, and they must return back to their old home if the Shadonian's are to survive.
However, little does everypony know, there is a new threat out there just waiting to strike.