This is the first episode since S6 E5 The Face of the Enemy (2018) which sees all four of Father Brown's helpers, Mrs McCarthy, Lady Felicia, Bunty and Sid Carter, brought together again.
This is the first time Lord Montague has actually been seen in an episode.
This is the 100th episode in the Father Brown (2013) series.
The events take place on New Year's Eve 1953.