Agatha Christie wrote The Mysterious Affair at Styles during the midst of World War I. The book was published in 1920 and became extremely popular because of the well-grounded plot and interesting characters. The novel is set at Styles Court, a wealthy estate in England during the war. The estate's owner, Mrs. Cavendish, had inherited the estate as well as vast sums of money from her late husband.

She goes on and remarries Alfred Inglethorp, and they live together with Mr. Cavendish's two sons, John and Lawrence Cavendish. John's wife, Mary, and Cynthia Murdoch also reside at the lavish estate. Mrs. Cavendish, now called Mrs. Inglethorp, is surrounded by people who will inherit the money and estate upon her demise. Not surprisingly, she dies of poisoning, and foul play is suspected.

This mystery novel is filled with twists and turns that involve the inspector, Hercule Poirot, who must look for clues as to who was responsible for Mrs. Inglethorp's death. Since the crime might affect the carrying out of the will, Poirot is under pressure from the entire household to figure out the truth. But just before she died, Mrs. Inglethrop is heard arguing with someone and is rumored to have made another will that would overrule any previous wills. However, that will is nowhere to be found. Through ingenious reasoning and careful planning, the culprits are finally caught, all thanks to the inspector.