The ordered calm of Gloucester Abbey is shattered by the murder of one of the monks. The Abbey becomes paralysed with fear and the Abbot is ill-equipped to deal with such a heinous crime, especially as suspicion inevitably falls on the brothers themselves. Ralph Delchard, a former soldier in the era-defining Battle of Hastings, and Gervase Bret, an accomplished lawyer, are investigating a local land dispute when news of the vicious murder reaches them. Before long, Delchard and Bret realise that the killing is just a symptom of a sinister presence that threatens the whole community and must be stopped at any cost.