Loving the Highland Warrior by Michelle Miles

Three pieces of stone. Two ancient bloodlines. One divine destiny.
Chloe Sinclair is desperate to find her sister who vanished under mysterious circumstances. Retracing her footsteps the day of her disappearance, she finds nothing but dead ends. Until she makes her way to an antique store in the heart of Edinburgh with an eccentric shopkeeper who gives her a strange looking stone and a cryptic message. When the man she thought she loved attacks her to take the stone for himself, it transports her back in time to medieval Scotland, dropping her in the middle of dangerous territory.

Malcolm MacLeod is faced with a deadly mission—a raid on his rival clan. But when he finds a lovely lass in the midst of battle, he has no choice but to rescue her and take her back to his clan. Upon his return, he realizes she possesses part of the missing ancient keystone he and his brother vowed to protect.