Three children are massacred in their beds. The crushed corpse of the mother is discovered in a dockside warehouse. Hanno Stiffeniis, a Prussian magistrate, goes to investigate, intending to apply the 'philosophical method' he had learnt four years earlier from Immanuel Kant. But everything begins to unwind. Serge Lavedrine, a criminologist attached to the invading French army, steps in to resolve the mystery, and Stiffeniis is packed off to collect the husband from a remote fortress on the Russian border. But the husband, Bruno Gottewald, is dead and buried - killed while out on field manoeuvres. In less than a week the entire Gottewald family has been wiped off the face of the earth. A tragic coincidence or are the French using the massacre to expand their power? Eventually, working independently of each other, Lavedrine discovers how the crime was committed, while Stiffeniis uncovers the motive behind the massacre. But only his wife, Helena, knows what truly happened in that cottage in the woods ...