Blood Ritual — Sarah Rayne

The descendants of Elizabeth Bathory, a bloodthirsty Hungarian countess who terrorized the Carpathian countryside in the 16th century, are determined that her line shall not die.   

Only Catherine, a paternal descendant, has tried to escape the terrible legacy that she has grown up fearing and detesting.  Eventually, she enters a convent, hoping to find the peace she has long desired.  But when she meets journalist Michael Devlin, she is drawn back to the ancient castle in the Carpathian mountains.  For Michael, who is haunted by the last thing he saw before losing his sight, is determined to discover the truth about the line of the infamous Elizabeth Bathory...  The lady that history had named The Blood Countess.