The Blackheath Poisonings — Julian Symons

From the day he moved to Blackheath and built the two eccentric mansions, Charles Mortimer had a run of bad luck. Decades later, in the 1890s, his ancestors in the mansions suffer the same unlucky fate. Roger Vandervent dies suddenly, followed by matriarchal Aunt Harriet. Suspecting murder, Roger's son, Paul, plunges into a nightmare of family greed, adultery, and secret sexual aberrations.