Fangs Over Cardington

From publisher blurb: An unexpected letter arrived addressed to the Commander. She has assigned you to investigate the author of the letter. Ms. Bella Davor, a debutant in exile, claims to be of ancient origins and cursed with a blood disease that prevents her from physically aging. She is being pursued by Echelon agents who wish to study her unique physiology. Her petition for asylum in Burgundia must be evaluated. You and your team are to verify her claim while preventing enemy agents from foiling your efforts.