In Scot Water by Caroline Lee

Malcolm Oliphant is, beyond a doubt, the brains of the family. Since his father, the laird, announced whichever brother could marry and produce a son first would become the heir, Malcolm’s brothers have been running around, falling in love willy-nilly, without using their brains at all. But not Malcolm, oh no. He plans to do this intelligently.
He’ll find a widow with a son or two, thus proving her ability to bear male offspring, and explain to her they will be married. See? Simple. No need to bring emotions into it.
But when he finally meets the perfect woman for his plan, there’s no logical explanation for the way his heart keeps getting involved. It would be so much simpler if the stupid organ would just simmer down, but have you ever tried explaining things to a hunk of meat, whose sole purpose is moving blood around?Impossible! Besides, when Evelinde looks at him, he feels like…a hero.

Evelinde Oliphant’s situation is getting desperate. Since her first husband’s death, she and her two sons are living alone in what could charitably be called the middle-of-bloody-nowhere, without any real means of support. When a scholarly warrior–one who makes her heart pound with desire–saves her life, how can she not think of him as her very own savior?
Falling in love–and into Malcolm’s arms–is the easy part. But what will happen when she learns who he really is, and why he really married her?