A body of a journalist about to expose an offshoot of the Freemasons, The Owl of Minerva, is found dead in the woods. Inspector Sullivan's investigations find him on the run for killing a fellow detective and seeking sanctuary in the confessional at St Mary's. Father Brown, with the aid of Mrs McCarthy, Lady Felicia, and Sid, rally round to try prove his innocence and protect him from a deadly organization with members highly placed in the community.