Dark in the City of Light — Paul Robertson

The climate is tense in 1870s Europe as mistrust and suspicion rule the day. When the wife of Baron Harsanyi--a well-connected military attache--is found murdered, it is only the first in a series of evil acts committed by a shadowy enemy bent on destroying the baron. As nations ready for war, the baron must uncover the truth as he and his two adult children are launched straight into the maelstrom that will engulf the continent.