Moll, a young nun, lies recovering from a migraine in the infirmary at St Mary's Priory, Belstone. Left to rest, she is just falling into a doze when she suddenly awakes, realising in terror that she can't breathe . . .
It's 1321 and Lady Elizabeth of Topsham, prioress of St Mary's, is struggling to retain her position in the face of devastating opposition. Sister Margherita, her treasurer, has accused her of lascivious disregard, claiming that Elizabeth has given money needed for essential repairs to the new vicar, a man she often sees alone - at night. Many of the nuns are convinced that Margherita would make a better prioress - especially now it has been confirmed that Moll was murdered.
Sir Baldwin Furnshill, Keeper of the King's Peace, together with his old friend Bailiff Simon Puttock, are summoned to investigate. There is no doubt that the threefold vows of obedience, chastity and poverty are being broken with alarming frequency. When a second nun is murdered, they find that their search for the killer, obstructed by the sinister forces of primitive passions and secret ambitions, finally leads them to a dangerous wolf in sheep's clothing.
