The early days of Bunty, before she took over the whole show, were a sign of things to come. Bunty (Emer Kenny) is like a show within the show. She does as she pleases, and she has no fealty to Father Brown.
Bunty was staying in town with Lady Felicia due to her bad reputation and shady activities at the private girl's academy where she had been expelled. Unfortunately, when Bunty arrives on the show, the much better characters of Lady Felicia (Nancy Carroll) and Sid (Alex Price) were phased out as regular characters on the show.
Perhaps worse is Jack Deam and his horrible acting as Inspector Mallory. Even after several seasons on Father Brown, Jack Deam is incapable of adding any nuances to his interpretation of the character. He plays it as just a nasty little guy who is always degrading everyone he talks to and yelling at Father Brown. Jack Deam is dreadful to watch.