Believers in the theory of nominalism have set some Cambridge colleges at the throats of those who believe them to be heretics, and Brother Michael, the Senior Proctor, is struggling to keep the peace. When a nominalist is murdered during a riot, Michael is certain he will find the killer among the Dominicans—but before he can act, his junior proctor, Walcote, is found hanged. Meanwhile, Matthew Bartholomew discovers evidence that leads to Michael himself. Unable to believe his lifelong friend could be capable of such acts, Bartholomew knows that the only way he can quiet his own conscience is to solve the murders himself.