In Bed with a Spy — Alyssa Alexander

Revenge has never been so seductive.

When her husband is killed at Waterloo, Lilias Fairchild takes up his cavalry sword and boldly storms the front, earning herself the nickname Angel of Vengeance. But there is another angel on the battlefield who is just as single-minded, and just as ruthless...

Alastair Whitmore, the Marquess of Angelstone, is a British spy. Code name: Angel. Still haunted by a first love felled by assassins, his mission draws him to Waterloo, where he is captivated by a beautiful and mysterious woman fighting amongst the men -- a woman who becomes his most intoxicating memory of war.

Passion has never been so dangerous.

Two years later, Lilias and Angelstone lock eyes in a crowded ballroom and the memory returns in an exhilarating rush. The history they share, and hide from the world, is as impossible to ignore as the heat of their attraction. But it's that very connection that spells doom for their scandalous affair. When someone from the shadows of their past proves a dire threat to their lives, passion might not be enough to save them.