A strange accident has stranded three mighty warriors in Equestria: Horus Lupercal, Sanguinius, and the Emperor of Mankind. Trapped in the bodies of ponies, and fresh from the battle on the Vengeful Spirit they must navigate this strange new world. But their very arrival has altered the course of Equestrian history: Nightmare Moon has escaped her end, and still haunts Equestria. With Horus at large with her, and the Emperor crippled by his injuries, Sanguinius must work with Twilight Sparkle to find a way to save the world, while maybe learning a few valuable (and grudging) lessons about friendship.