Seducing the Enemy by Noelle Adams

Having lived a sheltered life, Marietta Edwards wants to indulge in pleasures that are entirely new to her, so she begins by seducing a sexy, mysterious stranger.  Only after their one-night stand does she learn their families have been embroiled in a fifteen-year legal battle and the man she's given herself to is her worst enemy.

The heir to a vast fortune, Harrison Damon believes the unforgettable night he spent with Marietta in Monte Carlo is just a fling, an escape from his responsibilities. Then he discovers she is an Edwards—the family he despises most.

He can’t quench his attraction for her, but he won’t let her use it against him. He won’t let her manipulate him to win money from his family. No matter how much he wants her, he won’t let her seduce him again.