The Nabob's Designing Daughter. The Upstart Christmas Brides, #4

A wealthy nabob's daughter has designs on a handsome young doctor, but not the romantic sort, despite the one kiss he stole from her ages ago. The poor crofters she's been tending behind her father's back need more than a rich miss's potions, they need a real doctor. And fortunately, she has the leverage to provide one. Ripped from his prestigious London practice to deliver a Highland duke's heir, a young doctor finds there are more snares awaiting than a risky birth, including a surprise-and worthless-bequest.
There's also his best friend's cousin, who's blossomed from mousey to heart-stirringly beautiful, with enough wiles to convince an ambitious man that his heart belongs in the Highlands.