Trivia: This episode features the only appearance of a real human face in the series: when Lady Penelope peeps through a spyhole in the door of a bank during the opening scene. The face you see is that of puppet operator Judith Shutt, who was also Penelope's hand double throughout the series.
Trivia: Apart from Virgil Tracy, David Holliday provided the voice of just three 'guest' characters during the first series.
Trivia: At the beginning of this episode, we see Chip Morrison being put to bed by his father. Chip was last seen as Bob Williams in 'Cry Wolf', whereas his father previously appeared as Dave Clayton in the episode 'Day of Disaster'.
Pit of Peril - S1-E2
Trivia: Only five regular characters appear in this episode - Jeff, John, Scott, Virgil and Brains. This is the smallest number of regular characters seen in any Thunderbirds episode.
Trivia: When Prescott is driving along in his car, he is humming the song "Marina" from "Stingray", another Gerry Anderson show.
Trivia: In Thunderbird 5, a short piece of Barry Gray's "Formula Five" track can be heard. This was composed and recorded for another Gerry Anderson creation, "Fireball XL5".
Trivia: This was the last episode in which David Holliday voiced Virgil Tracy. He was replaced by Jeremy Wilkin for the second season. Some sources say that Holliday left because he had to return to America, while others say he demanded more money.
Trivia: This is the only Thunderbirds episode to feature the entire regular cast and all five Thunderbird craft.
Trivia: In this episode, Alan Tracy's voice is completely different from the one heard for the rest of the series. In his single, short line of dialogue, Alan is voiced by Ray Barrett, as Matt Zimmerman had not been employed when voice recording commenced (although he is credited in the end titles).
Trivia: When Virgil places the asleep Chip into his own bed towards the end of the episode, look behind Virgil and you can see a WASP Arrowhead Fighter Model from "Stingray" on the shelf by the window.
Trivia: The disaster of this episode is caused by a lightning strike damaging the automatic signals of a monorail train, causing it to speed towards a collapsing bridge. In 2011, a similar incident occurred in Wenzhou, China, when a lightning strike caused the railway's signals to mark a section of track as safe, despite containing a stopped train. A second train then entered and collided with the stopped vehicle, and derailed from the elevated track onto the fields below.
Trivia: The Doctor who visits Tracy Island at the end of the episode can also be seen reading a newspaper in the Departure Lounge at London International Airport.
The Duchess Assignment - S1-E21
Trivia: The Domo is a recycled version of the Excavator, which was used in the episode "Martian Invasion".
Trivia: The Zombites' jet fighters are adapted and re-sprayed WASP aircraft from "Stingray".
Trivia: This episode features extensive flashback footage from "End of the Road", "Sun Probe", "Trapped in the Sky" and "Day of Disaster", and only 17 minutes of new material. The reason for this is because the previous two episodes, "Attack of the Alligators" and "The Cham-Cham" had gone over budget and a flashback episode was required to finish the show's first season.
Pit of Peril - S1-E2
Trivia: This is the first episode to have an on-screen title.
