In this three-part episode, John Williams portrays an inspector investigating the death of a man portrayed by Anthony Dawson. Three years earlier in the Alfred Hitchcock film Dial M for Murder (1954), John Williams portrays an inspector investigating the death of a man portrayed by Anthony Dawson. They would both appear again in Midnight Lace (1960), directed by David Miller, with John Williams again portraying an inspector, but this time Anthony Dawson portrays a creepy stalker.
When Inspector Davidson talks to Raines about his having recently passed out of "Hendon", he is referring to Hendon Police College, in Hendon, north London. It is the principal training centre for the Metropolitan Police.