Secret Protector by Ann Voss Peterson
Hired to protect Natalie Kendall at any cost, Gray Scott intended to keep a low profile. But when his cover was almost blown he moved to plan B: become her boyfriend. Being so close and personal to the lovely heiress certainly allowed him to keep her safe, though the disguise was perhaps a little too tempting.
The bodyguard knew Natalie's nightmares were the key to unlocking the mystery of the Christmas Eve Murders. But she'd kept those secrets hidden for almost twenty years, and it would take more than his strong will to make her remember. It might just take the truth.