The Highlander’s Captured Bride by Eloise Madigan

Amidst the darkness of chaos, she was his heaven and his sin…

Violet O’Cain has been solving cases alongside her father ever since she turned of age. When they receive a letter from the Laird of MacChoill, requiring their services, she is not prepared for the scene she sees. Or the sadness in the eyes of the victim’s brother.
With vengeance on his mind and his brother’s killer still roaming free, Ethan MacFerson’s guilt stems elsewhere: his sudden inability to control himself around the detective’s beautiful daughter.
Convinced that his brother’s killer will strike again, Ethan’s suspicions are proven right. A note, with a very clear ultimatum: his head or his father’s. When Violet bears witness to something she shouldn’t have, she finds herself thrown into the dungeons, staring straight into the murderer’s eyes.