This episode contains many "Easter egg" references to previous episodes, to commemorate the 20th anniversary of the Midsomer Murders episode.
When Celeste Palmerston changes the radio from Midsomer Classic to Midsomer Folk Rock, the song playing is Dollhouse Blues by Hired Gun from episode 10.4, The Axeman Cometh (2007).
When Sarah Barnaby (Fiona Dolman) is starting to mark Circulus tests, the song The Ballad of Midsomer County is playing on Midsomer FM. This song is from episode 17.3, The Ballad of Midsomer County (2015).
Musical nods to The Curse of the Ninth (2017), The Ballad of Midsomer County (2015) and The Axeman Cometh (2007).
The pub is called The Green Man, the title of episode 7.1, The Green Man (2003). It was DS Troy's last episode.