Where There’s a Duke, There’s a Way by Emily E.K. Murdoch

Arthur Hebblethwaite, Duke of Fitzpaine is in rather a pinch. Firstly, he’s not actually a Duke.
It was such a clever idea. Pretend to be a duke, go to France, and live on the scraping and bowing of those desperate to impress a nobleman. All well and good, until someone recognizes him. Until he grabs a woman and uses her as a hostage to escape a French encampment. Until he looks at the woman and…oh, hell.

Joanna Bettencourt doesn’t know what’s worse: being a shy heiress with a father desperate to marry her off, being captured by the French and held prisoner, or being dragged onto a horse by a maniac by the name of the Duke of Fitzpaine. Pretending to have a husband ready to protect her seemed the obvious option.