Once a Laird by Mary Jo Putney

After the death of his fiancée, Kai Ramsay left Scotland to roam distant lands. He has searched ancient ruins, collected priceless antiquities, and escaped certain death after being imprisoned as a spy during the Napoleonic War. Ramsay has lived on the edge of danger for years—but everything changes the day a letter arrives for him from Scotland . . .
Signy Matheson has dedicated her life to the people of Scotland’s remote Thorsay Islands. With a fiery spirit and agile mind, she is a faithful ally to the aging laird. But now their leader is near death, and Signy must summon his successor at once. It’s time for Kai Ramsay to come home . . .
When Ramsay returns to Thorsay, he’s shocked to find that Signy has blossomed into an alluring beauty, and a force to be reckoned with. Their complicated past interferes with their unspoken desire as they work together for their people. Until a wild storm sparks first passion, then unexpected danger when a treasure trove left by their ancestors comes to light . . .