McLayne, Alyson. Sons of Gregor MacLeod.

A betrothal. A betrayal. A love threatened by treachery. Laird Callum MacLean vowed to marry Maggie MacDonnell. But when his father's apparent suicide makes him Laird of his clan, Callum must unmask his father's killer before bringing Maggie into his dangerous new home. Maggie's home isn't any safer. When Callum fails to return, Maggie does what any resourceful Highland lass would do. She escapes--and finds herself toe-to-toe with Callum, who's determined to fulfill his promise. Maggie can't bring herself to trust him with her heart again. But with a traitor still at large, they must rely on each other in every way, or their clans--and their love--will be destroyed