The words at the top of the book that traps Jamie and Zoe translate from French into "A Fox: Trapped."
Although she appears until the end of the season, this episode is where Wendy Padbury's contract first ended. She was only contracted until the end of the fifth production block, which concluded with this story, and a new contract was needed for the sixth.
Peter Ling wanted Zorro to appear, but this was vetoed for copyright reasons. A quotation from Walter de la Mare's 1912 poem The Listeners seems to have been excised due to similar concerns.
This episode was watched by 6.7 million viewers on its original transmission.