The Rock by Monica McCarty

The first time he caught sight of Elizabeth Douglas, Thomas MacGowan thought she was a princess. To the son of the castle blacksmith, the daughter of the powerful Lord of Douglas might as well be. When it becomes clear that his childhood companion will never see him as a man she could love, Thom joins Edward Bruce’s army as a man-at-arms to try to change his lot. If he’s harbored a secret hope that he could close the gap between them, he faces the cold, hard truth when Elizabeth comes to him for help. She might need the boy who used to climb cliffs to rescue her brother from the hands of the English, but she would never see the son of a smith as a man worthy of her hand.