Inspector Mallory pursues a cop killer holed up in an isolated house. However Sergeant Goodfellow takes a bullet for him and Mallory injures his shoulder.
With Alan Tylett, the alleged cop killer still at large, Scotland Yard sends in Inspector Truman to investigate.
Father Brown is familiar with him. Better known as Inspector Sullivan now also working to root out dirty cops.
This time Sullivan is happy to partner up with Father Brown. Maybe because he cannot trust other policemen. A notebook that Mallory came across containing a list of names has disappeared. This list may had contained the names of bent coppers.
This was an enjoyable episode with an ending that leaves Sullivan thinking if he has done the right thing.
It does have the problem of another policeman who suddenly appears at the police station that you have never seen before. It was good to see Sullivan being more amiable with Father Brown this time. There was also a sweet moment as Mallory thanks Goodfellow who lies unconscious in the hospital bed.
You do wonder though if Mrs Mallory ever wondered where her husband has been for the last few days?