Christie was born into a wealthy upper-middle-class family in Torquay, Devon. Before marrying and starting a family in London, she had served in a Devon hospital during the First World War, tending to troops coming back from the trenches. She was initially an unsuccessful writer with six consecutive rejections,[4] but this changed when The Mysterious Affair at Styles, featuring Hercule Poirot, was published in 1920.[5] During the Second World War, she worked as a pharmacy assistant at University College Hospital, London, acquiring a good knowledge of poisons which feature in many of her novels.

Agatha Mary Clarissa Miller was born on 15 September 1890 into a wealthy upper-middle-class family in Torquay, Devon.[14]:1 She was the youngest of three children born to Frederick Alvah Miller, an affluent American stockbroker, and his British-born wife Clara Miller née Boehmer.[14]:2–4