Agatha Christie put her decision to become a writer down to a lack of education and a capacity for day-dreaming. Her murder mysteries, full of ingenious plot twists, are still regarded by many as the finest examples of crime fiction and have sold in their billions in the English language and in translation.

Although the world she depicts is considered by some to be cosy and genteel, and her plots formulaic, a new generation of screenwriters is bringing out the darker side of Christie’s imagination. So what accounts for her continuing global success, when today’s crime fiction tends to be grittier and more realist?

Bridget Kendall is joined by Dr Michelle Kazmer, Professor in the School of Information at Florida State University, who’s combined a lifelong passion for crime fiction with study into how we use information – such as clues or evidence; Dr Mark Aldridge, Associate Professor of Film and Television at Solent University and the author of Agatha Christie on Screen and Poirot: The Greatest Detective in the World; and James Prichard, Agatha Christie’s great-grandson. Award-winning crime writer Ragnar Jónasson also explains how Agatha Christie's novels influenced his own work.

Produced by Fiona Clampin for BBC World Service.