No humans. In Equestria's past, ponies exist only to serve their creators. One such pony is accidentally released from her mental chains, but how can one mare save herself and her people if she doesn't even know she's a slave?
Princess Celestia makes a visit to a new world, Earth, to cement peaceful relations. Unfortunately, even when you are as experienced as the goddess of the sun, it's the little things that can trip you up.