Because old scars never heal. Because ponies aren't always as nice and friendly as they appear. Because you can never outrun your demons no matter how hard you try.

When a dark stallion named Scourge stumbles into Ponyville, he makes friends and seems relatively nice. But he may not be completely sane. Something always seems to bother him. Now dark entity lurks in the shadows, waiting for just the right moment to get it's vengeance and bring all of equestria crashing down.