Puhak is a poet and the author of “The Dark Queens,” a rousing account of two sixth-century Merovingian sisters-in-law who wielded enormous power while alive only to be maligned after their deaths. “The Blood Countess” is a similarly hybrid work of true crime and feminist history. Puhak draws from archival research to lay out how received wisdom has been warped over the centuries by exaggerations, shoddy scholarship and outright fabrications. Her book takes the tale of one woman and turns it into a portrait of an era.