Quietly in their sleep

Commissario Guido Brunetti comes to the aid of a young nursing sister who has had five patients unexpectedly die and decides to leave her convent. In the course of his inquiries Brunetti encounters an unusual cast of characters but discovers nothing that seems criminal. Is the nun simply creating a smoke screen to justify abandoning her vocation? Or has she stumbled onto something very real and very sinister-something that places her own life in imminent danger?