With love, Harry

In which Harry goes back in time, adopts his arch nemesis and pulls one infamous Dark Lord into his madness somewhere along the way. "Surprise! Tom, meet your grandfather!" "Harry. That's Gellert Grindelwald." "I know. Isn't it exciting? And he'll be tutoring you to be the greatest Dark Lord ever!" "What?" TimeTravelAU. MOD!Harry. NOT SLASH.