The narrative opens with Prosper, a young clerk in Paris who believes his fortune is made after marrying and securing a post near the Bishop of Beauvais. On the morning the victory of Rocroy is celebrated, a catastrophic clerical error leads the Bishop to believe Prosper deliberately forged a population census to mock him. Stripped of his position, beaten by grooms, and cast into the street, Prosper suffers a complete inversion of his safe, modest life.
While fleeing the scene, Prosper stumbles upon a desperate man who thrusts a bundle into his arms—which Prosper soon discovers is the four-year-old King of France, stolen from the Louvre. Terrified by the weight of this secret, Prosper attempts to find his father-in-law at the Palais Royal, but is rejected as a madman. Meanwhile, a reward of five hundred crowns is offered for the return of the Queen-Regent's missing pet dog, Flore, rather than the King, though the two mysteries quickly become entangled through political intrigue.
Driven by a thirst for vengeance against the Bishop, Prosper tracks the missing dog to an empty house in the Montmartre Faubourg. Here, he encounters mysterious agents of Cardinal Mazarin, who are orchestrating a political chess match against the Bishop's faction, known as the Importants. The agents coerce Prosper into playing a dangerous role: he must recover the dog and restore it to the Queen, securing the reward while indirectly undermining the Bishop's standing at court.
Prosper succeeds in returning the animal to the Queen-Regent in the ante-chamber, amid the presentation of Flanders colours. When the Bishop claims credit, Mazarin sets a subtle trap by asking the dog to perform its old tricks. The animal fails to recognize the Bishop's commands, utterly discrediting him before the court and cementing Mazarin's rise to absolute power.
Following the court drama, Prosper finds himself targeted by the Bishop's vengeful steward. However, Mazarin's silent agents intervene, granting him a purse of twenty crowns and directing him to start anew in Rouen. Prosper leaves Paris as an exile, but his quiet obedience ultimately lays the foundation for a prosperous future in the royal chancery, echoing the broader triumph of Mazarin over his rivals.
The volume concludes with supplementary historical episodes, including 'Crillon's Stake,' where a daring nobleman wagers his life at dice to save a reckless youth, and 'For the Cause,' a tale of Huguenot resistance and devotion during the religious conflicts of Paris.
