The Hellion and the Hero by Emily Sullivan

Rafe Davies might seem like just another charismatic rake, but in reality, he is one of the crown’s most valuable agents. As relentless as he is reckless, Rafe has never come upon a mission he couldn’t complete. But when he encounters the intriguing-yet-prickly lady’s companion Miss Sylvia Sparrow while on assignment at a Scottish house party, he finds himself thoroughly distracted by the secretive beauty.
Though most women would be thrilled to catch the eye of a tall, dark, and dangerously handsome man, Sylvia is through with that sort of adventure. She trusted the wrong man once and paid for it dearly. The fiery bluestocking is resolved to avoid Rafe, until a chance encounter between them reveals the normally irreverent man’s unexpected depths—and an attraction that’s impossible to ignore. But when Sylvia begins to suspect she isn’t the only one harboring a few secrets, she realizes that Rafe may pose a risk to far more than her heart.