Diary of a Murderer — John Matthews

New York City, 1891. Aristocratic English pathologist Finley Jameson Jameson and streetwise New York cop Joseph Argenti begin their second adventure together investigating a high society poisoning case. But when the daughter of a prominent banker dies in broad daylight from a sudden heart attack, the case takes a curious turn. Jameson and Argenti investigate deeper to see how many high society deaths from disease might actually be murder.

This investigation sends a worrying ripple through New York high society, since as much as families want to know the truth, a death by natural causes is more acceptable than a serial killer preying on high society girls. 

As their investigation intesifies, and the sinister link between the victims emerges, Jameson and Argenti worry the question isn't if there is a serial killer, but if there is more than one.