Throughout the episode, Steed keeps making phone calls about purchasing some polo ponies. In the last scene, Steed refers to someone important who might try the outbid him for the ponies. This was a reference to Prince Philip who was an active polo player at the time.
Interesting to note that this episode contained 3 Dr. Watsons: André Morell appeared as Watson along side Peter Cushing in Hammer's "Hound of the Baskervilles" 1959. Patrick Macnee played Watson 3 times; Sherlock Holmes in New York with Roger Moore, then "Sherlock Holmes and the Leading Lady" (1991) and "Sherlock Holmes: Incident at Victoria Falls" (1992) with Christopher Lee as Holmes. David Burke played Watson with Jeremy Brett in the first season "The Adventures of Sherlock Holmes" 1984-1985.
The original script had Wrightson's estate at the extraordinary figure of £480,000, which was revised to a more reasonable - if unattainable - £180,000.
£180,000 in 1963 would be about £4,648,000 now (November 2023). That equates to about $5.8 million.