Gwen Donavan adores her beautiful and rebellious older sister, Izzy. But the Izzy who returns from the Delphi School for Girls is not the sister who left. Now she is Isolde: dull and complacent and--most shocking--eager to marry.

Gwen is determined to discover what happened to Izzy at Delphi, and the only solution she can conceive of is to cheat her way into the mysterious school. If she can see for herself what they did, maybe she can get her Izzy back.

But Delphi is far from the finishing school Gwen expects. Sinister shadows lurk in the hallways of the remote estate, and she is told to never leave her room after dark. More curious, though, are the thousands of books, each with the name of a girl on its spine. They line the walls from floor to ceiling, and the students are forbidden to read them.

Delphi says they're reforming the girls, but when Gwen discovers a note left for her by her sister, she realizes that what is happening at the school is more terrifying than she could ever have imagined. There's something dark at the center of Delphi, and somehow it's tied to those books--and to the girls who are sent there. And if Gwen doesn't confront what hides in the shadows, it won't be just Izzy who's lost forever.