In Alyssa Alexander's In Bed with a Spy, the second book in Alexander's Spy in the Ton series, both of the protagonists are fighting in the Napoleonic Wars—the heroine, interestingly, wields a sword in battle whereas the hero is a spy, code name Angel.
At first, Angel, aka Alastair Whitmore, Marquess of Angelstone, feels happy when he spots the lovely Lilias Fairchild in the ballroom, remembering her from Waterloo, a warrior woman seeking to avenge the death of her soldier husband by taking the field herself. Now, two years later, Lilias also recognizes Alastair, though their eyes met only briefly on the battlefield. The two manage to escape the unwanted attentions of hopeful suitors and debutantes to go outside to the balcony, enjoying each other’s company, flirting and using a double entendre that amuses them both.
However, when Lilias leaves, Angel discovers a coin on the ground, realizing it remained after the spilled contents of Lilias’s purse had been picked up. To his shock, Angel recognizes a medallion with the symbol of the Death Adders, a group of assassins. As a spy, Angel has a direct interest in bringing the Death Adders to justice, but the desire goes deeper for him, as his former lover and fellow spy was murdered by one of them. Intent on discovering Lilias’s involvement with the organization, Angel devises a plan to find out.