In Cambridge, barely recovered from the great plague of 1350, a series of crimes occurs. The first victim is the city prostitute Isobel Watson, then the corpse of an unknown monk is found in a locked chest with the university archives. Matthew Bartholomew, who is investigating these crimes, during the exhumation of the body of the university clerk Nikolos in the grave, instead finds another corpse, again female, with a terrible goat mask on his head. The matter is complicated by the fact that there are two communities of devil worshipers in the city, as well as a gang of criminals led by Janetta, a ruthless woman with a scar on her face. In addition, the local sheriff is doing everything possible to prevent Bartholomew from getting on the right track...