An unholy alliance - Susanna Gregory

In 1350 the people of Cambridge are struggling to overcome the effects of the Black Death.
Bands of outlaws roam the land and the high death rate among priests and monks has left the people vulnerable to sinister cults that have grown up in the wake of the plague.
At Michaelhouse Matthew Bartholomew is training new physicians to replace those who died of the pestilence.
When the body of a friar is found in the massive chest where the University stores its most precious documents, Bartholomew is dragged away from his teaching to investigate.
But the friar's is not the only unexplained death in town.
Almost by chance Bartholomew stumbles across a derelict church, abandoned since its congregation were decimated by the plague.
It is now the meeting place for a mysterious sect which holds its followers in terror, and which Bartholomew believes to be at the very heart of an astonishing web of blackmail and deceit aimed to overthrow the established religion.