The Mysterious Affair at Styles - 1920

Agatha Christie's debut novel, as well as the first appearance of the great detective Hercule Poirot. Mrs. Emily, the mistress of Styles Court, is in charge of the financial power of the house. She died of poison in her room one morning, and the three doors to the room are locked from the inside. In the investigation, Poirot found fragments of a burned will, broken coffee cups, clothing fibers, large areas of candle oil, etc, that point to every suspect. The biggest suspect in the case --- the husband --- has an alibi. The doctor is suspicious and her children also have motives. In the narrative, everyone seems to be the murderer, yet no one has conclusive evidence of guilt.