This is the story of the fall of an Empire – and the rise of another. Who spread Christianity, how, and why? In her quest to find the answer, Professor Alice Roberts takes us on a gripping investigative journey. From a secluded valley in south Wales to the shores of Brittany; from the heart of the Roman Empire in a time of political turmoil to the ancient city of Corinth in the footsteps of the apostle Paul; from Alexandria in the fourth century to Constantinople.