One day, Twilight Sparkle was in the Royal Canterlot Library. She found a strange book there…

The Great War with Discord cost the Royal Pony Sisters dearly. All their kind, bar themselves and a pair of brothers, were lost to Chaos' fell claws. Worse still, under the corruption of Nightmare Moon, Luna left Celestia alone as the only alicorn alive in all the world. The brothers, whom both princesses loved dearly, vanished in a magical attack and were never seen again.

Now the world is a very different place. Luna has returned and been purified, Discord is no longer behaving badly (much), and not one, but two more alicorn princesses have graced Equestria with their presence. On the surface, Equestria seems a far happier place than it has been of late.

But as tension rises with the neighbouring Griffon lands, and with another, far older threat lurking unseen in the background, ponykind may be facing their direst peril yet.

And meanwhile, in a small field outside Ponyville, a pair of brothers return to Equestria on a Night of evil and Nightmares, and go hunting for the one responsible…