The Orchid Affair (Pink Carnation #8) by Lauren Willig

Laura Grey, a veteran governess, joins the Selwick Spy School expecting to find elaborate disguises and thrilling exploits in service to the spy known as the Pink Carnation. She hardly expects her first assignment to be serving as governess for the children of Andre Jaouen, right-hand man to Bonaparte's minister of police. Jaouen and his arch rival, Gaston Delaroche, are investigating a suspected Royalist plot to unseat Bonaparte, and Laura's mission is to report any suspicious findings.