The Guardian by Jo Jones

Kiss me…quick!
After centuries stuck on Culloden Moor, Marcus Beaton is anxious to use his newfound freedom to explore the world. He’s ready to see new things and maybe even discover a great new adventure.
Tait Keller – at least that’s the name she’s currently using—is alone and running for her life. Even Witness Protection has failed to keep her safe. She has choices to make and no one to trust.
She needs a Guardian. But is Marcus all he appears to be?
Helping Tait could be far more than Marcus bargained for. And what could a three-hundred-year-old Highlander—completely out of his element—do to save her, that trained U.S. Marshalls couldn’t?
Only three days left, and a puzzle with missing pieces. Will they find them in time?