There's Always Tomorrow (Immortal #1)

1810
Anthony Bowles and his best friend, Thomas Pinkerton, were young, rich, and foolish; but never as foolish as their last night in the ancient city of Prague. They should have taken heed of the warnings they’d received before starting out under the light of the full moon. Convinced the stories of monsters devouring the innocent were nothing more than figments of overactive imaginations and terrifying tales told to naughty children, they left the protection of the city streets and ventured deep into the woods.
It was that single act that would change their lives forever—for all eternity.

2011
Sophie loved her job. Working for a handsome and mysterious private investigator was always exciting. One never knew who’d stumble through their door, or where their inquiry would take them. One afternoon, he walked through the door and turned her life upside down by telling her a fantastical story; a tale so bizarre, only a woman in love would believe it. Sophie never questioned his veracity and agreed to follow him anywhere in search of his life-long quest. No matter what they discovered, she was confident their love would endure throughout the ages.