The year is 1803, and England and France remain at odds. Hoping to break the English once and for all, Napoleon backs a ring of Irish rebels in uprisings against England and sends the Black Tulip, France's most deadly spy, to the Emerald Isle to help. What they don't know is that England's top spy is also in Ireland: the Pink Carnation, who is working to shut the rebels down.

Meanwhile, back in England, Letty Alsworthy intercepts a note indicating that her sister, Mary, is about to make the very grave mistake of eloping with Geoffrey Pinghingdale-Snipe (second in command of the League of the Purple Gentian). In an attempt to save the family name, Letty tries to stop the elopement, but instead finds herself swept away in the midnight carriage meant for her sister and is accidentally compromised. Geoff and Letty, to each other's horror, find themselves forced into matrimony. Then Geoff receives word that he is to travel to Ireland to help the Pink Carnation; he disappears immediately after their ceremony. Letty learns of Geoff's disappearance and, not to be outdone by her husband, Letty Alsworthy steals away on a ship bound for Ireland, armed and ready to fight for her spouse and to learn a thing or two about spying for England.

As in her previous tales, The Secret History of the Pink Carnation and The Masque Of the Black Tulip, a modern-day heroine and hero, Eloise Kelly and Colin Selwick, continue their budding romance in this captivating third novel in the series.