The MacGregor’s Lady by Grace Burrowes

What if the steps they take to avoid marriage…

The last thing Asher MacGregor, newly titled Earl of Balfour, wants is a society wife, though he has agreed to squire Boston heiress Hannah Cooper about the London ballrooms. When he’s met that obligation, he’ll return to the Highlands, and resume the myriad responsibilities awaiting him there.
…Lead instead to impossible love?
At her step-father’s insistence, Hannah Cooper must endure a London season, though she has no intention of surrendering her inheritance to a fortune hunter. When she’s done her duty, she’ll return to Boston and the siblings who depend upon her for their safety… or will she? The taciturn Scottish earl suits her purposes admirably—until genuine liking and unexpected passion bring Asher and Hannah close. For if the Scottish earl and the American heiress fall in love, an ocean of differences threatens to keep them apart.