Subtle Blood. The Will Darling Adventures, #3

Will Darling is all right. His business is doing well, and so is his illicit relationship with Kim Secretan--disgraced aristocrat, ex-spy, amateur book-dealer. It's starting to feel like he's got his life under control. And then a brutal murder in a gentleman's club plunges them back into the shadow world of crime, deception, and the power of privilege. Worse, it brings them up against Kim's noble, hostile family, and his upper-class life where Will can never belong.
With old and new enemies against them, and secrets on every side, Will and Kim have to fight for each other harder than ever-or be torn apart for good.