When it comes to love, some lines are meant to be crossed True, US Secret Service Agent Liam Harper is charming, handsome, and absolutely devoted to the people and things he cares about—including his job protecting the vice president's moody son, Mason. But Emily Harper can't let Liam's good qualities cloud her judgment. As the sister of a Secret Service agent, she knows that Liam's job could mean taking a bullet, and she's vowed never to get romantically involved with someone in that line of work. Agent Harper knows he's been friend-zoned, but that doesn't stop him from falling for Mason's petite and plucky physical therapist. She never fails to put the privileged teen through his paces, yet she manages to make the kid like her all the same. And that Southern drawl is nearly intoxicating when she lays it on thick. But when Mason enters the crosshairs of a killer, Emily and Liam will find the lines between professional and personal are about to get awfully blurry.