States of Grace: A Novel of the Count Saint-Germain (St. Germain)

Franzicco Ragoczy di Santo-Germano is a successful merchant in Venice. His lavish lifestyle and rumored cache of magnificent jewels have attracted the wrong sort of attention, and without Santo-Germano's noble―and papal―connections, he might be imprisoned, his property confiscated. Also under surveillance is the vampire's mistress, the lovely and talented musician Pier-Ariana Salier.
Elsewhere, Ragoczy's publishing business is being investigated by the Inquisition. Erneste van Amsteljaxter, a writer whose intelligence Ragoczy finds attractive, is tarred with the brush of heresy. Ragoczy is trying to help her, when he learns that Pier-Ariana has disappeared.
Back in Venice Santo-Germano finds that his fortune has been embezzled, and that he is accused of kidnapping, and possibly murdering, a young man who had been spying on the vampire and his mistress. Another spy has discovered Santo-Germano's true nature and intends to kill him before he can feast on all of Venice!