Gavin by Hazel Hunter

Though his body is healed, a modern-day vet in medieval Scotland must find a way to mend his heart.

Though Gavin McShane is happy for his sister and her new life, his own has foundered. As he tries to recover from his lover’s betrayal, he finds solace in the work of being a fisherman in the Orkneys. On his tiny island he finds relief in seclusion—until he meets the ghostly Blue Lady of Marr.
Young druidess Catriona Haral is no phantom. But her hidden existence has made her seem so, even to herself. When Gavin wanders into her secret glen, she wonders if she’s found a reason to want to live again.

But Catriona wasn’t hiding on a whim. When her reasons are revealed, the might of the McDonnel clan and the judgement of the druids land at her doorstep.