Nicolas Le Floch is suspected of poisoning Julie de Lastérieux, his mistress, and finds himself in a rather unpleasant situation where he must investigate to clear his own name. He learns from Monsieur de Sartine that Julie worked for the King's secret service. It would appear that Julie was killed to compromise her lover. The King, whose trust in Le Floch remains unshaken, takes him away from the dangers of the investigation and sends him on a mission to London.
—Happy_Evil_Dude