In The Mysterious Affair at Styles, Emily Inglethorp, the elderly owner of Styles Court, is found dead in the morning hours. She has been poisoned with strychnine and the killer is assumed to be one of the residents of the Styles house.

The story begins when Hastings is sent back to England from the First World War due to injury and is invited to spend his sick leave at the beautiful Styles Court by his old friend John Cavendish. Here, Hastings meets John's step-mother, Mrs Inglethorp, and her new husband, Alfred.
When Mrs Inglethorp is murdered, Poirot uses his detective skills to solve the mystery.