I Spy a Duke — Erica Monroe

She wants revenge… When bluestocking Vivian Loren becomes the governess for the wealthy Spencer family, she's searching for clues about the murder of her brother, not a husband. But Vivian didn't count on James Spencer, the infuriatingly handsome Duke of Abermont. He needs a wife… As head of Britain's elite intelligence agency, James has no time to woo a wife. When he discovers Vivian's quest for answers has made her a pawn in a treacherous plot, James realizes they can help each other. She'll become his duchess, and he'll keep her safe from one of Napoleon's deadliest spies. What begins as a marriage of convenience quickly becomes anything but, as they find out love is the most dangerous mission of all.