The Wicked Heir by Mary Lancaster

False engagement – or true love?

From the age of thirteen, Jess has been brought up by her irascible and reclusive guardian, Lord Viscral. Sheltered but spirited, Jess finally rebels when his lordship decides out of the blue that she should marry his estranged son and heir, Jonathan, whom she has never even met. Jess immediately makes plans to run away with the assistance of her childhood sweetheart and make her living running a hat shop.
But this is Blackhaven, where things rarely work out as planned. Lord Viscral has come to take the waters and to entice his black sheep of a son back into the fold, with Jess as bait. The black sheep, however, has no intention of being caught by either of them. Captain of a famous merchant ship, he only wishes to see that his father is well. However, when he encounters Jess out of her depth in a gaming hell, he is intrigued.
And sees the possibility of an alliance to punish his tyrannical parent.
Of course, it isn’t that simple. Jess’s sweetheart turns out to have feet of clay and brings more problems than he solves. Someone is stealing Jon’s cargo. Someone else is trying to kill Jess and Jon. Cousin Hector alternately scolds and proposes.
In the middle of it all, Bonaparte escapes from Elba, Jon begins to suspect blood is thicker than water, and worst of all, learns that it’s far too easy to fall in love with Jess…