Book excerpt: The heiress of Styles has been murdered, dying in agony from strychnine slipped into her coffee. And there are plenty who would gain from her death: the financially strapped stepson, the gold digging younger husband, and an embittered daughter-in-law. Agatha Christie's eccentric and hugely popular detective, Hercule Poirot, was introduced to the world in this book, which launched her career as the most famous and best loved of all mystery writers.