The Sign of Nun

The Sign of Nun is the third in the series of Dave Harris Murder Mysteries. It is the story of a serial killer who is active on the campus of a large university.Can the police protect the student body or must they take it upon themselves?
The killer has a fatal flaw. What is it? Can the police use it to uncover the identity of the murderer? Will a secret code expose the criminal,who can break it?