After being driven out of Ponyville following the incident with the Ursa, The Great and Powerful Trixie flees into the Everfree forest, where she meets a mysterious masked stallion named Herald. Herald offers Trixie a chance to learn ancient magic that will truly make her the most powerful unicorn in Equestria, by offering her a book that not even Twilight Sparkle has ever read. But there is a reason Twilight's never read this book, and there is more to Herald than there appears...

(A Cthulhu Mythos crossover. Cover art by kirokokori. TVTropes page here, although I've no idea who started it, and was gobsmacked when somebody else told me http://tvtropes.org/pmwiki/pmwiki.php/FanFic/TheStarsWillAidTheirEscape )