Derpy Hooves is could easily be cast out of society because of her wall-eyed look, even so she didn't really care about it until now when she meets Lightning Dust an old classmate from school who always bullied her.
Dusk isn't like any other pony for she is only half of one the other is best remained secret but when a familiar evil arises it lays squarely on her shoulders to save Equestria but at the cost of showing herself to the world