In 1793, Hanno Stiffeniis travels to Konigsberg to seek advice from Immanuel Kant. Whatever was said at that private meeting, it changed both their lives. Shortly afterwards, a close friend of the philosopher extracts a promise from the young man: never to return to Konigsberg. But ten years later, having become a magistrate, Stiffeniis is ordered to return there by the King. He must investigate a spate of murders which has reduced the city to a state of terror. Four people have died, and there is no sign of an end to the killing spree. Tension inside the city is heightened by the imminent threat of invasion: Napoleon is menacing the borders of Prussia. While hunting for a murderer in the criminal underworld of Konigsberg - forced to deal with scheming whores, necromancers who claim to speak with the victims, and the scum of the Prussian army - Stiffeniis is caught up once again in the enigmatic world of his former mentor, Kant. What demons haunt the magistrate's past and why has he had been enticed back to Konigsberg to deal with these grisly murders? Stiffeniis must face a dark truth which he would rather deny...