Dr. Stickney: Are you the Jason King who writes the Mark Caine books?
Jason: Yes.
Dr. Stickney: Oh. Now that I have met you, I must read one of them sometime.

Stewart: My, my. Guards at a health hydro.
Jason: Very common.
Stewart: With dogs?
Jason: Well, it keeps the frenzied guest from breaking out and hurdling toward the nearest bar.

Jason rescues Halliday at night (about 10:30 p.m. according to Stewart's watch); however, there are several shots during the escape scene that show the sun out.

A close-up of Stewart's watch shows the date as the 10th. According to the opening, the event began on the 20th of April. Halliday was in his boarding room for seven days (which would have been April 27th), then kidnapped. The timeframe in the story would have put the date no later than April 29th, not the 10th of May.

One scene shows Halliday's badly burned left hand; however, none of the other scenes in the episode show his hand as damaged.

Halliday's car is the same car that Jeff Randall used in the series Randall and Hopkirk (Deceased). Both shows were in production by ITC at the same time.