Good and evil, light and dark, right and wrong, this binary pervades our thinking. This weekend is Halloween, originally a date in the Christian calendar but also a much wider holiday now in which all things dark are celebrated, and next week is Diwali, the Hindu festival of lights, a celebration in part of the triumph of good over evil. But the very ideas of good and evil pose difficult questions. What is evil? And what happens if we don't agree over it? Almost all people see themselves as ultimately good, so where does evil fit into the picture? And why evil exists at all is one of the most ancient questions of theology explored by thinkers through history. Joining Azim Ahmed to discuss all this are: Muslim theologian and philosopher Dr Safaruk Chowdhury, author of a monograph on “the problem of evil”; Rev Dr Helen Hall, Anglican priest and senior law lecturer at Nottingham University who has advised the C of E on exorcism; the Brecon-based Hindu teacher philosopher and theologian Akhandadhi Das, and Rev Dr Jason Bray, vicar of St Giles, Wrexham and a practicing exorcist.