Agatha Christie 
How Does Your Garden Grow? 

An old woman named Amelia Barrowby sends Poirot a strange letter explaining that she needs his services. In her message, she insists that discretion is essential because her family could be involved. The detective agrees and proposes a meeting, but he does not hear from his client again. Five days later, the newspaper announces the death of Miss Barrowby. Hercule Poirot will visit her house and investigate the family until he discovers the whole truth.