When Gloriana agreed to cohost a formal dinner with her uncle, she did not know she was about to discover a plot to overtake her country. The pampered and sheltered young heiress soon found herself squeezed by several vises: Europe and Mexico, Church and state, liberal and conservative. The battle at Puebla on the Cinco de Mayo is by all accounts a minor skirmish, but one which electrified he world. That Napoleon's army should be routed by a ragtag...