The murder of women priests in the shrine town of Walsingham sucks Dr Ruth Galloway into an unholy investigation.

When Ruth's friend Cathbad sees a vision of the Virgin Mary, in a white gown and blue cloak, in the graveyard next to the cottage he is house-sitting, 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 Cathbad's vision was all too human, and that a horrible crime has been committed. DCI Nelson and his team are called in for the murder investigation, and soon establish that the dead woman was a recovering addict being treated at a nearby private hospital.

Ruth, a devout atheist, has managed to avoid Walsingham during her seventeen years in Norfolk. But then an old university friend, Hilary Smithson, asks to meet her in the village, and Ruth is amazed to discover that her friend is now a priest. Hilary 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...