The Historian, by Elizabeth Kostova.
Here's a thought: we have moved out of the era where historians and horror movie fans are two entirely different sets of people -- there's enough overlap to justify this book, after all. The plot (which successfully pulls off almost as many stories-within-stories as The Arabian Nights) involves a naive young woman inquiring into the history of her father, a scholar who was pulled into researching the legends of Dracula after finding a mysterious book. So. Lots of history, lots of horror, and lots of the even darker area where they intersect:
"For all his attention to my historical education, my father had neglected to tell me this: history's terrible moments were real. I understand now, decades later, that he could never have told me. Only history itself can convince you of such a truth."
The book is well written (for some reason, I kept comparing it to Jonathan Strange and Mr. Norrell, as in "almost as good as"), the characters are interesting, and I feel like I gained a real insight into the fascinations of history (vs. fiction). The ending wasn't handled as well as the rest of the book, and I had to roll my eyes at one point -- I'm sure that it's nothing that would bother most people, but I hate that kind of ending, so, like many of the characters in the book, consider yourself warned.