This is a superb exploration of, not just the literary vampire/slayer dynamic, but the etymological history of vampires and vampire myths in the Eastern European setting that spawned them. While it could possibly read as dry, tracing the history and usage of the word "vampir" reveals the function of re-animated corpses as scapegoats within agrarian societies. McClelland also traces the transformation of the original ideas of vampires and vampirism into the Western European literary vampire we know today.
The history/etymology of slayers follows the same path, first looking at the original cultural origins and significance of people designated by a community to see/slay vampires, then follows the concept of eradicating vampires into Enlightenment Western Europe. It then looks at more modern cultural representations of slayers such as Van Helsing from Dracula, Kolchak the Night Stalker, Mulder and Scully, and (of course) Buffy the Vampire Slayer.
All in all, this book is an excellent overview of the origins of the vampire myths, their transformation into the cultural mythos we know today, and the function of "slayers" within those myths. As both a historical work and a cultural analysis this work is top-notch for getting a handle of vampire history and origin, as it addresses pre-Christian history and local custom, and doesn't treat everything pre-18th century (i.e. before the rise of the literary vampire) as vague and unknowable, as if vampires sprang up during the Enlightenment without any previous existence.