Prisoner of Memory by Denise Hamilton
This is Hamilton's fifth Eve Diamond novel, and I think it's the best. A young Russian man turns up on Eve's doorstep claiming to be her long-lost cousin, Mischa. Of course, Eve is skeptical, but then she becomes involved in a case that is connected to Russia: the death of a boy of Russian heritage, which may be linked to the Russian Mafia, or to his family's past, or both.
While investigating this case, Eve starts researching her own heritage, something she has previously avoided. Of course, the things she learns about her family's past include some things she'd rather not know.
Eve is becoming an interesting, well-rounded character, and I'm looking forward to seeing her grow as the series continues.