The Duke in Question by Amalie Howard

James Bond meets Bridgerton in this steamy enemies-to-lovers historical romance from bestselling author Amalie Howard:
This lady won’t let a savvy duke sway her from her mission.
The Duke of Thornbury, retired agent of the Crown, has never lost a target.
In a flirty game of cat and mouse, a spy must keep his enemy close to unravel the secrets that threaten to tear them apart.
Lady Bronwyn Chase is far from the paragon of society that her mother expects her to be. Which is why she’s on her brother’s passenger liner bound for America with a secret packet of letters that could get her into trouble. Serious trouble—the kind that a duke’s sister shouldn’t be in; the kind that puts spymaster Valentine Medford, the Duke of Thornbury, on her trail. But as the duke gets closer to Bronwyn and the secrets she’s keeping, he’ll have to decide between the mysterious woman who calls to him, or his allegiance to the Crown.