Servetius Drindle sat at his ornate lectern, his head in his hands. He had taught generations of Hogwarts students the basics of defense against the dark arts. It was he who had convinced the ministry of magic to include the summoning of magical and mystical beings of varying alignments in the curriculum, and had made evocation a respectable discipline in the magical world again. The best practices manual for evocation of spirits? Almost entirely his work. The pencil pushers and bureaucrats assigned to the committee were more of a hindrance than a help. Every evocationist in the magical world was a product of his program. Or they were, anyway. Now they were all dead, except for his best student, Mercutio Bindersmith. Mercutio, who described himself as a "huge Voldemort nerd." A harmless hobby, Servetius thought, and a fascination with Voldemort was almost a standard part of the edgy magical teen starter pack.
Voldemort, after all, had been dead for more than a century, his power broken, and his feared Death Eaters dead or in hiding. But then Mercutio had the brilliant idea of summoning Voldemort (perhaps it was time to start calling him "He Who Is Not To Be Named" again?) and interviewing him for a feature in The Daily Prophet. He succeeded. The Voldemort he succeeded in contacting seemed to be a changed… being. Congenial, with a pleasant, self-deprecating sense of admitted that mistakes had been made, and that some of his beliefs about "mud bloods" had been misguided. But it didn't end. Mercutio became secretive. Then, his colleagues in the evocation world started having mysterious accidents, or being caught in perverse and horrifying acts.
To make a long story short, Mercutio was now Voldemort, and vice versa. And he commanded an army of what could be described as the evil dead, and a significant proportion of the evil undead. Some of these were former colleagues and friends. And as for the living inhabitants of the magical world, well… Some of them were straight-up death-eaters. Most of the others were not, but pointed to Voldemort's undeniable organizational skills and his sincerity.
Now, Servetius was all that stood in the way of Voldemort's total domination. His friends were depending on him for their very lives. After all, if he could summon spirits, he could banish them. He had written the manual! But there was one problem. Two, actually. Servetius had never actually done magic. Also, draftsmanship was very important in producing the magical sigils and circles crucial to evocation, and Servetius couldn't draw. He had always hired others to do the illustrations for his textbooks.