Richard Delancey is soon called into action once more, as Britain prepares for the threat of a new French assault. Disturbing rumors are circulating about Napoleon's new weapons of war: vessels driven by steam-engines, new explosive devices, and, most troubling of all, a French secret weapon named Nautilus, which can travel underwater and attach explosive devices below the waterline. It will take all of Delancey's skill and courage to confront the threats.