A Scoundrel in the Making by Tarah Scott

Retired spy Abigail Matheson has inherited the title of Marchioness of Buchman upon the death of her cousin. The title, which he’d inherited from her father, should never have been hers. But that annoyance is forgotten when The Raven, Abigail’s superior, introduces her to Sir Stirling James. They request her assistance on one final mission: find the stolen crown jewels of Scotland.
Abigail accepts this unexpected opportunity in hopes of forgetting the young French spy she killed on her last assignment. When The Raven and Sir Stirling inform her that she will be working with Lord Reade, a rake of the first order, Abigail, who’s always worked alone, plans to ignore the partnership and complete this mission alone.

Lord Reade, brother to Robert Murdock, the Earl of Kinwall, has been given the opportunity to gamble with men who can afford to lose a lot of money. And a lot of money is exactly what Reade needs if he is to save his family’s ancestral home from creditors and prevent his brother’s family from being forced onto the streets. The catch: he must work with a beautiful spy to find the thief who stole the Honors of Scotland. Surely, he can ignore her long enough to salvage his family’s fortune. The string of suitors determined to be the next Marquess of Buchman prove too much a distraction, however, and Reade is forced to take matters into his own hands.