A student is murdered in the college gardens. Soon after a mayor is killed with a sabre. Copenhagen is haunted by additional murders, and the cases fall into the hands of Professor Thomas of Boueberge.

Are the crimes perpetrated by Swedish spies, as many believe? People are terrified, and the town smoulders. Violence and chaos in the streets force the despotic king to fight fire with fire. Thomas of Boueberge endeavours to find a pattern. Who is responsible for these crimes? Thomas receives support from his assistant Petter Hortten, his friend Ludvig Holberg, and not least by a youth named Petter Wessel. To top it off, a close friend of Thomas and Petter is killed. They are both thrown in jail, and Thomas suffers torture. When he eventually puts two and two together and reveals who is guilty of the murders, no one is prepared to believe him.