During one take of the scene where The Doctor is fishing, Tom Baker inadvertently tossed the antique fishing rod he was using into the water. Stunt arranger Terry Walsh had to dive in and rescue it.
The plot is based on that of the 1894 adventure novel "The Prisoner of Zenda".
Mary Tamm designed Romana's distinctive outfit after the originally planned costume by Doreen James proved to be made of scratchy tweed. It was done up in Mary's favorite colors at the time, purple and teal.
While Doctor Who (1963) opening credits are typically ordered story title-author's name-episode number, this story's order was story title-episode number-author's name.
The Doctor had been planning a holiday when first recruited by the White Guardian, a running joke being that whenever he sets off on a holiday he never gets to enjoy one.