It’s in his Highland Kiss by Shona Thompson

He brought her war, she gave him peace…
Lady Marion Hadlee seems like an obedient daughter, although she harbors a desperate secret. No one knows she is planning to kill herself to escape her parents’ abuse. Being saved by a dashing Highlander wasn’t part of her plan.
His interference gives her a chance at a new life.
Eiric McLeod is an elite spy, unraveling secrets as Scotland plans a rebellion. His investigation takes him to a ball full of English enemies where he crosses paths with a raven-haired girl about to take her life.
Intrigued by her beauty and sadness, he takes her to the Highlands.
There, Marion is transformed. From a wallflower, she becomes an enchantress—a spy in Scotland’s service with a mission of her own. She uses her feminine charm to entrap a powerful Englishman.
Now, Eiric must watch the woman he desires seduce another man. His heart tells him to stop her, but his loyalty to his country won’t permit him to react.
And in this war between heart and logic, there cannot be a winner…
He saved her life, she saved his soul…