A Vow of Silence — Veronica Black

Sister Sophia was dead.
Sister Magdalen had vanished.

Strange things are happening in Cornwall Convent, and most disconcerting to Sister Joan, who has been transferred there to quietly investigate the convent's mysterious troubles, is that the Prioress wears pink nail polish and perfume. She has also forthrightly inquired as to whether Sister Veronica, the beautiful young novice who has traveled down with Sister Joan, is a virgin.

More--and more deadly--departures from normal convent routine are yet to come. Whispered hints dropped by other nuns...frantic searches for a missing novitiate...a secret midnight service in the convent chapel. Sister Joan begins to suspect what she hardly dares to name. But it is much too late to withdraw. Too late even to send for help...