When Morse visits his mother's grave, it can be seen that his mother's date of death is 1950. As Morse was twelve at that time, his birth date must therefore have been 1938, making him 27 at the time of this story.
When Joyce asks Morse why he returned to Oxford, she says that his dad just said "Proverbs 26, 11".
In the Old Testament, Proverbs chapter 26, verse 11 says "Like a dog that returns to its vomit, the stupid one repeats his foolishness."
In this story, Morse encounters his cold and unpleasant stepmother Gwen, who was also featured, as a much older woman, in the Inspector Morse" episode "Cherubim and Seraphim", played by a different actress (Edwina Day).
One of the pseudonyms used by the dead girl is said to be "June Buckridge" - the central character in Frank Marcus's play "The Killing Of Sister George", a great West End success at the time this episode is set and later filmed (in 1968) with Beryl Reid repeating her stage role.
Judy Vallens describes herself jokingly as a "Matildabeast", meaning a student of St. Matilda's, the (fictional) Oxford college which features strongly in a "Lewis" episode set over forty years later, "Old, Unhappy, Far-Off Things", and is mentioned importantly in the later "Endeavour" story "Muse".