Determined to secure another London season without assistance from her new brother-in-law, Mary Alsworthy accepts a secret assignment from Lord Vaughn on behalf of the Pink Carnation: to infiltrate the ranks of the dreaded French spy, the Black Tulip, before he and his master can stage their planned invasion of England. Every spy has a weakness, and for the Black Tulip that weakness is black-haired women - his 'petals' of the Tulip. A natural at the art of seduction, Mary easily catches the attention of the French spy, but Lord Vaughn never anticipates that his own heart will be caught as well. Fighting their growing attraction, impediments from their past, and, of course, the French, Mary and Vaughn find themselves lost in the shadows of a treacherous garden of lies.