Enchanted by the Highlander by Lecia Cornwall

Gillian MacLeod is shy and quiet, the least likely of all her sisters to seek out excitement and adventure. But on a moonlit night at a masquerade ball, Gillian steals a kiss from a mysterious stranger, knowing she’ll never see him again.
John Erly, disowned by his noble English father, started a new life in Scotland. Most people are suspicious of the foreign mercenary and he does everything is his power to avoid romantic entanglements. But he can’t forget the bewitching beauty who kissed him in the dark, and stole his heart, even though he has no idea who she might be.
A year later, John is given the duty of escorting Gillian to her wedding and immediately recognizes her as the temptress he’s dreamed of for months. There’s not much he can do when she’s promised to another man, but fate intervenes and this time, passion—and adventure—can’t be denied. Honor demands he stay away from the MacLeod’s enchanting daughter, but love has a very different ending in mind…