21 June, 1815. London may be cheering the news of Napoleon's surrender at Waterloo, but Lady Petra Forsyth has little to celebrate after discovering that the death of her viscount fiancé three years earlier was no accident. Instead, it was murder, and the man responsible is her handsome, half-Scottish secret paramour Duncan Shawcross--yet the scoundrel has disappeared, leaving only a confusing riddle about long-forgotten memories in his wake.

So what's a lady to do when she can't hunt down her traitorous lover? She concentrates on a royal assignment instead. Queen Charlotte has tasked Petra with attending an event at the Asylum for Female Orphans and making inquiries surrounding the death of the orphanage's matron. What's more, there may be a link between the matron's death and a group of radicals with ties to the aristocracy, as evidenced by an intercepted letter.

Then, Petra overhears a nefarious conversation with two other men about a plot to topple the monarchy, set to take place during three days of celebrations currently gripping London.

As the clock counts down and London's streets teem with revelers, Petra's nerves are fraying as her past and present collide. Yet while all's fair in love and war, she can never surrender, especially when more orphaned girls may be in trouble. And to save their lives, the monarchy itself, and even her own heart, Lady Petra must face her fears with the strength of an army of soldiers and fight with the heart of a queen.