Just as the Sisters in a Toronto religious convent are about to bury one of their own, they see that there is already a body in the grave. Det. Murdoch investigates but is shocked to find that his sister Susannah is the Mother Superior. They had not seen each other for 20 years when she left for convent school as a 14 year-old eventually joining a cloistered order. She had received a dispensation from her vow of silence and has been in Toronto for five months, something that disturbs William as she had not contacted him. The dead man was wearing a clerical collar but is later identified as a crook with a criminal record. Murdoch finds the place on the convent grounds where the man was murdered and is convinced that the killer is to be found among the religious sisters.