Father Brown - Season 1 Episode 10

When the notorious thief Flambeau declares his intention to steal a valuable blue cross from the church, Father Brown, against the advice of Valentine, decides to take it to safety to Newbury abbey by train. He meets a trio of fellow passengers, one of which he is sure is the thief but his efforts to flush him out lead to the theft of the cross. Facing dismissal for his rash action the Father agrees to meet with Flambeau and do a deal to return the artefact.