Forbidden sister - Virginia Andrews

I had every reason to hate her, my forbidden sister. She was like someone who had died but wouldn't stay buried . . .

Emmie Wilcox was only six when her older sister, Roxy, was thrown out of their New York City apartment. Their stern father's military-style rules left no room for rebellion, and Roxy was as defiant as Emmie-now an outstanding student at a private school-is compliant: a perfect daughter, une fille parfaite, as her Parisian-born mother lovingly calls her.

Two sisters, total opposites-yet Emmie is secretly obsessed with the mystery surrounding Roxy: What had she done? Where is she now? And is there a hidden side to Emmie that resembles Roxy's spiteful nature? Knowing only that Roxy is a highly paid escort to the city's wealthiest men, Emmie goes behind her father's back to track down the sister she fears, despises, and inexplicably clings to . . . and whose influence might run deeper than Emmie ever imagined.