The Deception of the Emerald Ring — Lauren Willig

Harvard grad student Eloise Kelly has gotten into quite a bit of trouble since she's been spying on the Pink Carnation and the Black Tulip--two of the deadliest agents to saunter the streets of nineteenth-century England and France. Not only has she been unearthing secrets that will rearrange history, but she's been dallying with Colin Selwick and looking for a romantic adventure all her own. Little does she know that she's about to uncover another fierce heroine running headlong into history.

In June 1803, Letty Alsworthy attempts to prevent her sister's midnight elopement--only to be accidentally whisked away herself. The scandal forces her into a hasty marriage with Geoffrey Pinchingdale-Snipe, who then decamps immediately to help the Pink Carnation quash a ring of Irish rebels led by the Black Tulip. Not to be outdone, Letty steals away to the Emerald Isle herself, ready to learn a thing or two about espionage and never imagining she might learn a few things about love along the way.