The three villains are Earl, Stanley and Gardener, the name of
The creator of Perry Mason
Sir Arthur Doyle is a blatant send up of Sir Arthur Conan Doyle. He is even dressed like Sherlock Holmes complete with a deerstalker cap and a pipe.
In Noon Doomsday, Steed is forced to rest in a farm because of a broken leg, but in this one and The Joker, both Tara and Steed respectively can stay home.
Tracy Reed and Edward de Souza were previously teamed in the Edgar Wallace thriller The Main Chance (1964)
This is one of few plots in which Steed's flat is never seen, with Mission Highly Improbable, Fear Merchants, EPIC, Take-Over, All done With Mirrors, Interrogators, They Keep Killing Steed, Bizarre and Take To Your Leader.
This is one of few plots in which Espionage or Betrayal are not implied at all, instead it only show blackmailers.