If your pulse flutters at the thought of castle ruins and descents into crypts by moonlight, you will savor every creepy page of Elizabeth Kostova&apos,s long but beautifully structured thriller The Historian. The story opens in Amsterdam in 1972, when a teenage girl discovers a medieval book and a cache of yellowed letters in her diplomat father&apos,s library. The pages of the book are empty except for a woodcut of a dragon. The letters are addressed to: "My dear and unfortunate successor." When the girl confronts her father, he reluctantly confesses an unsettling story: his involvement, twenty years earlier, in a search for his graduate school mentor, who disappeared from his office only moments after confiding to Paul his certainty that Dracula-Vlad the Impaler, an inventively cruel ruler of Wallachia in the mid-15th century-was still alive. The story turns out to concern our narrator directly because Paul&apos,s collaborator in the search was a fellow student named Helen Rossi (the unacknowledged daughter of his mentor) and our narrator&apos,s long-dead mother, about whom she knows almost nothing. And then her father, leaving just a note, disappears also.