Ancient secrets buried deep in Glastonbury's past. And one woman's quest to finally set them free. Cambridge present day: Following the death of her mother, Abi Rutherford receives a mysterious bequest -- a misshapen sphere of crystal known as the Serpent's Stone which seems to hold echoes of concealed mysteries, long covered up by the church. Western England 25AD: A stranger has come to the chilly Somerset wetlands, with a story of hope and reconciliation. But he is being followed by powerful forces, determined that he will not undermine Roman rule in Britain. What connects these ancient events and Abi's gift? And why do so many people seem desperate to hide the truth? A strange shadow has fallen across the centuries, and a woman is in fear of her life. But is it danger that awaits her, or the final truth so long whispered across the echoes of time?