Schulmeister and his wife settle in the Château du Piple, a gift from the Emperor in gratitude for his services. Behind the wall of a cellar, he discovers the corpse of an unknown man, deliberately placed there to trigger an investigation by Schulmeister and his friend Hammel. They uncover a scheme orchestrated by the Prussian envoy, intended to disrupt the secret negotiations between Fouché and Sir Horace, the representative of England.