Silent in the Grave by Deanna Raybourn
It's London, 1886. To say I met Nicholas Brisbane over my husband's dead body is not entirely accurate. Edward, it should be noted, was still twitching upon the floor...For Lady Julia Grey, her husband's sudden death at a dinner party is extremely inconvenient, not to mention an unpardonable social gaffe. However, things take a turn for the worse when inscrutable private investigator Nicholas Brisbane reveals that the death was not due to natural causes. Drawn away from her comfortable, conventional life, Lady Julia is exposed to a dark and threatening new world...This sparkling, witty tale is the first in a captivating series featuring Lady Julia and Nicholas Brisbane.