Crimson Heart by Heather McCollum

As the illegitimate daughter of King Henry VIII, Elena Seymour has spent most of her life in hiding. Keeping her royal blood a secret has been a success for years, but now, with a new, fiercely Catholic queen on the throne, Elena’s Protestant caretaker is being targeted. And when Bloody Mary discovers Elena’s lineage, she must not only flee to Scotland for her freedom, but also for her life.
Highland warrior Searc Munro has secrets of his own. In a family of healers, his own dark, killing magic must never be known. But when his father’s life is threatened, Searc’s secret is revealed. No longer welcome in his clan, he sets off alone, only to find another use for his magic—to save a beautiful young lass being attacked in the forest.
Teaming up as exiles, Elena and Searc head toward Edinburgh to find refuge. Yet, with a series of ritual killings haunting the city and a traitor attempting to assassinate Scotland’s regent, suspicion turns to Searc as word of an illegitimate British heir reaches the country. Now, the two must find a way to trust each other, despite their secrets, before it’s too late.