Vampire, Interrupted (Argeneau Vampires, Book 9)

After seven hundred years of life, Marguerite Argeneau finally has a career. Well, the start of one, anyway. She's training to be a private investigator, and her first assignment is to find an immortal's mother. It seemed simple enough, until Marguerite wakes up one evening to find herself at the wrong end of a sword. Now she realizes she's in way over her head.
Julius Notte wants to protect Marguerite, and not because someone just tried to take her head off. She doesn't know it yet, but she's his lifemate and he's determined to woo her. It's been over five hundred years since he last courted a woman, but surely the techniques haven't changed. Now if only he can keep her alive—so to speak—so they can have that happily-ever-after.