When Thursday explains to Max that Ronnie Box has " ... come from robbery", Max replies, "Not the Lucie Clayton?". Max is alluding to the Lucie Clayton Charm Academy, is a finishing school for girls in the period of time in which the show was set.
The hidden message in the Masterpiece Theatre closing credits is "Anna Sewell," the author of the book "Black Beauty" which plays in important part in the plot.
The first episode of the "Endeavour" series upon which Roger Allam gets a credit as "associate producer" as well as for acting.
Red Leb or Red Lebanese is a reddish-brown light Hashish made from the resin of the cannabis plant.
This story sees the return of the foul-mouthed, racist, misogynist and blatantly incompetent Inspector Ronnie Box, played by Simon Harrison. Despite the shortcomings he demonstrated as an officer in last season's episode Passenger (2018), and the reprimand he received from Chief Superintendent Bright, he has now been promoted to Detective Chief Inspector.