On the orders of the Minister of Foreign Affairs, police commissioner Châtelet Nicolas Le Floch embarks on a life-threatening journey from Paris to Vienna in order to expose an enemy spy network that may even involve the resident French intelligence agent Abbé Georgel. At the same time, he must provide a report on the recent expansion of the empire's borders as far as Moldavia, as well as on the numbers and character of the troops stationed there. It is there that he will learn who organized the so-called flour riots in France.