Rules of Summer by Joanna Philbin

There are two sides to every summer. When seventeen-year-old Rory McShane steps off the train in East Hampton, it's as if she's entered another universe, one populated by impossibly beautiful people wearing pressed khakis and driving expensive cars. She's signed on to be a summer errand girl for the Rules -- a wealthy family with an enormous beachfront mansion. Upon arrival, she's warned by other staff members to avoid socializing with the family, but Rory soon learns that may be easier said than done. Stifled by her friends and her family's country club scene, seventeen-year-old Isabel Rule, the youngest of the family, embarks on a breathless romance with a guy whom her parents would never approve of. It's the summer for taking chances, and Isabel is bringing Rory along for the ride. But will Rory's own summer romance jeopardize her friendship with Isabel? And, after long-hidden family secrets surface, will the Rules' picture-perfect world ever be the same?