Guard of Honor by Tracie Delaney

A woman on the edge of insanity—or is something far more sinister at play?

A year ago, Honor Reid was kidnapped and held hostage for seventeen days. Freed in a ransom drop gone wrong, her ordeal has lasting consequences. Despite round-the-clock security, she lives in fear of her abductor returning to finish the job.
Royal Marine veteran, Aiden “Mack” McKenzie is struggling with his own demons. He isn’t interested in a babysitting job on the other side of the Atlantic, especially for a damaged billionaire heiress who point-blank refuses to leave her house.
When the man Mack owes his life to pleads with him to take the job, Mack reluctantly agrees. However, he gets more than he bargained for when he finds himself drawn to the woman he’s bound to protect.
Within days of his arrival, strange things start to happen, and Mack must face up to the possibility that the woman he’s falling for is not all she seems.