R. Austin Freeman 
As a Thief in the Night [EPUB ebook] 

Another brilliant mystery featuring the medico-legal forensic investigator Dr Thorndyke!
Harold is a patient found dead from arsenic poisoning, Amos his brother is left in no doubt that foul play is afoot. The inquiry begins and Harold’s wife is soon singled out as the prime suspect. What ensues is a roller coaster ride into crime fiction at its best as the truth of the fateful night eludes even the best of detective minds. Could it be a simple case of a wife poisoning her husband, or is it just possible that another shadowy figure stole into Harold’s room, as a thief in the night, to rid the world of an innocent man?