In 991, Vikings sail up the Blackwater Estuary and attack Maldon in Essex. Inside the church of St Mary the Virgin, a priest and a group of women anxiously await the outcome of the battle. In 1979, Dr Emma Stuart, a genealogist in London, is asked by a client from Denmark to trace a Viking ancestor who may have participated in the invasion. An eleventh century whetstone found on his farm has a puzzling inscription. She is intrigued and decides to investigate. Then, when her mother inherits a sixteenth century house in Norwich from an unknown relative, Emma's research begins to suggest possible links to her own past, links that began in a church at the Battle of Maldon.