Autumn, 1379. The power of the crown is invested in John of Gaunt, and the kingdom is seething with discontent. The French are attacking the southern ports and peasants are planning a revolt organised by a mysterious leader who proclaims himself 'Ira Dei', the Anger of God. His plans plunged into chaos by a series of bloody murders, Gaunt turns to Sr John Cranston to catch the assassin and recover a vanished king's ransom in gold. Together, Cranston and his ally, Brother Athelstan, face threats and attack from the powerful as well as the seedy underworld of medieval London as they attempt to bring a cunning murderer to justice.