Credo tells the story of a young Irish princess named Bega, and the two loves of her life - her God and a young nobleman called Padric - a lifelong tug between this earth and the next, romance and faith. The story is set in seventh century Britain, and Melvyn Bragg has really done his homework, describing life in Anglo Saxon times in rich detail. Many of the characters are based on historical figures too, St Bega being the main one, and the story hinges around real events. I personally found it very convincing, and a real insight into a particular place and culture, the Kingdom of Northumbria and Celtic Christianity.
It's quite a fascinating period in English history, and an important one in the story of Christianity, and Credo hits a satisfying balance between love story, adventure, and historical exploration. These were savage times, and Bragg doesn't gloss over the brutality. He doesn't dwell on it either, but sensitive readers should be warned that there are some genuinely horrible moments. My only real caution though is the length - at some 780 pages it takes some commitment to reach the end. But if you're a fan of epic novels and are willing to take your time, its a rewarding read.