The African poison murders

This mystery is set in East Africa (country not specified) just prior to World War II. It was written in the late 1930's and published in 1939. Author Huxley was brought up in this area and brings vivid and authentic description and characters to the story. Huxley is most widely known for her memoir The Flame Trees of Thika. The story is the third and last in a short series featuring CID Inspector Vachell. The story highlights the unrest prior to WWII, felt by both the German and English settlers in this part of colonial Africa. Inspector Vachell is brought in to investigate Nazi activities and several unsettling and gruesome local acts. Things are brought to a head when a local farmer dies. Is it murder or an unfortunate accident?