J. S. Fletcher 
Herapath Property 

When Jacob Herapath, the wealthy property developer, is found dead in his office, a revolver at his side and a bullet wound to the head, the time of death is placed a midnight. Remarkably, his driver left him off at his home an hour later where he consumed a scotch and several sandwiches. Something is obviously amiss. Add an allegedly forged will, the hint of an old family scandal, and a former secretary of the murdered man whose motives are none too clear, and the mystery only deepens. (Goodreads)