If there is no God watching us, why be good? Richard Dawkins examines sin. He asks whether the old religious rules about what is right and wrong are helpful and explores what science can tell us about how to be good. Dawkins journeys from riot-torn inner city London to America's Bible Belt, building a powerful argument that religion's absolutist moral codes fuel lies and guilt. He finds the most extreme example in a Paris plastic surgery clinic that specialises in making Muslim brides appear to be virgins once again. But what can science and reason tell us about morality? Through encounters with lemurs, tango dancers, the gay rights campaigner Matthew Parris and the scientist Steven Pinker, Dawkins investigates the deeper roots of moral behaviour in our evolutionary past. He explores the rituals that surround mating and the science of disgust and taboo. Drawing on crime data and insights from neuroscience, he argues that our evolved senses of reason and empathy appear to be making us more and more moral, even as religious observance declines.