When Ruth's friend Cathbad sees a vision of the Virgin Mary, in a white gown and blue cloak, in Walsingham's graveyard, he takes it in his stride. Walsingham has strong connections to Mary, and Cathbad is a druid after all; visions come with the job. But when the body of a woman in a blue dressing-gown is found dead the next day in a nearby ditch, it is clear that a horrible crime has been committed, and DCI Nelson and his team are called in for what is now a murder investigation.

Ruth, a devout atheist, has managed to avoid Walsingham during her seventeen years in Norfolk. But then an old university friend asks to meet her in the village, and Ruth is amazed to discover that she is now a priest. She has been receiving vitriolic anonymous letters targeting women priests - letters containing references to local archaeology and a striking phrase about a woman 'clad in blue, weeping for the world'.

Then another woman is murdered - a priest. As Walsingham prepares for its annual Easter re-enactment of the Crucifixion, the race is on to unmask the killer before they strike again...