Lily Lesser, who plays "Ravenna Mackenzie", is the real life daughter of Anton Lesser, "Chief Superintendent Reginald Bright".
The story takes place in November of 1968, something made clear towards the end when the main characters all start wearing Remembrance Day poppies in their lapels. (There is also a Remembrance Day service conducted by the headmaster of Coldwater school, when he speaks of the end of the First World War as being "fifty years ago").
The poem that Morse reads at the end is "Say not the struggle naught availeth", by English poet Arthur Hugh Clough (1819-1861).
Reading Grammar School (established in 1125) in Reading, Berkshire, features as the Coldwater public school in this episode.
Cromwell Ames's alibi for one of his crimes is that he was in London at the time "at the bunny club". The London Playboy Club had opened in London (in Mayfair, near the London Hilton Hotel) in 1966, a little over two years before the period in which this story takes place. It is still there in the 21st century, although much less high-profile than it was in the swinging '60s.