The Highlander’s Secret Avenger by Heather McCollum

Drostan Macquarie, the fierce battle-hardened Highlander, was still a young lad when his father first warned him of the ancient curse on the Macquarie clan. Should any of our kin sire a bastard, the entire clan will be cursed to die out. Drostan vowed then to live his life alone, far from the reach of the curse. But on the eve of Beltane, a sizzling kiss with a mysterious lass ignites Drostan’s blood…and threatens his vow.
Amelia MacLeod is on the run, desperate to escape her past, and an abusive family. But Wolf Isle isn’t just a place to hide, it may be her only hope of redemption—if she can doom her clan’s enemy, the Macquaries. Only, she imagined her enemy would be a hideous brute, not a big, brawny, and kind-hearted Highlander like Drostan.

Because now Amelia’s discovered a way to destroy the Macquarie Clan for good—if she can bring herself to infiltrate the clan, seduce Drostan, and bring about the Macquarie curse. Of course, she hasn’t accounted for the far-reaching consequences of her own dark past…or her traitorous desire for the Highlander she came to destroy.