Poirot's first case.

Invalided home from the First World War, Lieutenant Hastings finds himself in a convalescent home very much to his disliking. Thankfully his old friend John Cavendish invites him to spend the rest of his sick leave at his family home. The beautiful Styles Court is home to John’s step mother Mrs Inglethorpe, and her new husband Alfred. Despite the tranquil surroundings Hastings begins to realise that all is not right. When Mrs Inglethorpe is found poisoned a murder investigation begins, and who better to investigate than war refugee Hercule Poirot, a retired Belgian detective.
Christie’s favourite review of this, her first book, was from the Pharmaceutical Journal, which praised, “this detective story for dealing with poisons in a knowledgeable way, and not with the nonsense about untraceable substances that so often happens. Miss Agatha Christie knows her job.” It was adapted for television with David Suchet as Poirot in 1990.