Such is the cryptic note the archbishop receives after the funeral of Mother Rose. The nuns believe she died of natural causes and the archbishop sends Father Andrew Nolan-Andy-to identify the killer and then participate in a cover-up to protect the Church from scandal. Andy succumbs to the assignment only because if he refuses, his request for a dispensation from the priesthood to legally marry Mia (with whom he has been having an illicit affair) will be denied.

How will Father Nolan find a killer whose poison leaves no trace in the human system? How will he guide the nuns in their spirituality when he's secretly spying for the archbishop?