Quiet as a Nun (Penguin crime fiction)

In Antonia's Fraser's first work of fiction we meet Jemima Shore, a refreshing addition to the considerable list of investigators in the mystery genre. Jemima's first task is to solve a murder in the secluded tower at Blessed Eleanor's Convent in Sussex. The victim -- an old school friend -- left a puzzling note stating: "Jemima will understand what is going on here. Jemima knows..." But Jemima doesn't.